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The only thing more annoying than getting your period unexpectedly (usually on the day you wore your nice new undies/white pants)? Not having the slightest clue when it’s going to come.

While a period that’s a few days out is manageable, if it’s happening regularly it could be in response to something you’re going on in your body – or a sign of a bigger issue.

1. You’re pregnant.

“ Pregnancy is one of the most common causes of irregular periods, so it always needs to be excluded,” says Sapphire Medical Practice ‘s Dr Dasha Fielder.

The easiest way to rule this out is to do an at-home pregnancy test or to visit your doctor. In the mean time, note if your body is showing any other common symptoms such as tender breasts, the frequent need to go to the bathroom, nausea and fatigue.

2. Your contraception.

The contraception you use could offer an explanation as to why your period is being irregular.

“Birth control works to prevent ovulation by supplying the same dose of female hormones every day, and turns off natural production of sex hormones which avoids the surge in oestrogen and follicle stimulating hormone (FSH) required for ovulation,” explains Dr Fielder.

This is why people on the Pill can experience lighter, less frequent or even non existent periods. (Post continues after gallery.)

Popular forms of birth control

Intrauterine device

IUDs are small, T-shaped devices that are inserted into the uterus by a doctor in order to prevent pregnancy. There are two types of IUD: copper, which affects the movement and survival of sperm in the womb while changing the lining of the womb;and hormonal, which releases progestogen (a synthetic version of the naturally-occurring hormone progesterone) into the uterus. Although IUDs have a success rate of more than 99%, only around 2% of Australian women currently use one.

Vaginal ring

Vaginal rings are soft plastic rings that contain the same two hormones as the combined pill - oestrogen and progestogen. The ring is inserted into the vagina, where the hormones are absorbed into the body and then prevent the ovaries from releasing eggs. Once inside the ring can't be felt, and it needs replacing every three weeks (with one week's break in between). When used correctly, this method is more than 99% effective.

Contraceptive pill

The Pillis the most popular form of birth control. There are two types: the combined pill, containing two hormones, and theprogestogen-only, or mini, pill, which only contains one female hormone. The combined pill works by preventing the ovary from releasing an egg each month. The mini pill changes the mucus at the entrance of the uterus, which stops sperm from entering. Both are 99.7% effective; however, they don't offer protection from STDs.

Diaphragm

Like the male condom, the diaphragm is a barrier method of contraception. It's a shallow silicone dome that's inserted into the vagina andcovers the cervix, which is the entrance to the uterus. It's held in place by the pelvic muscles, and works by preventing sperm from entering the uterus. After sex, diaphragms need to remain in placefor another six hours, in which time the sperm inside the vagina die. This method is 88 to 94% effective at preventing pregnancy, although this rate increases with experience.

Condoms

The male condom is a barrier contraception that prevents both pregnancy and the transmission of STDs. They work by collecting semen so it doesn't enter theman's partner's body. Condoms are 95 to 99% effective at preventing pregnancy.

The female condom

The female condom is a pre-lubricated sheath, which loosely fits inside of the vagina. The condom has a removable ring, which helps to insert the sheath and keep the condom in place. A larger ring remains on the outside to cover the opening of the vagina. They are designed to fit all women and can only to be used once. Due to misuse of the product it is only 79 per cent effective.

Birth control implant

This is a 4cm-longimplant that is inserted into a woman's upper arm, just under the skin, by a doctor. It releases a hormone called etonogestrel, which prevents ovulation and thickens the mucus in the cervix, which can stop sperm from entering. Contraceptive implants - usually sold as Implanon - are removed under anaesthetic every three years, and are close to 100% effective.

Depo Provera

Depo is a long lasting hormonal injection. The synthetic form of progesterone is administered every 12 to 14 weeks to woman, preventing pregnancy within this ongoing time period. The injection, which is given in the buttock or muscle of the upper arm, prevents ovulation and thickens the mucus in the cervix, helping to block sperm. The injections are 99 per cent effective but do not protect against STDs. Male contraceptive injections are currently being trialled

The morning after pill

Emergency contraception (popularly referred to as the morning after pill) is used to prevent a pregnancy following unprotected sex. Other reasons include missing a contraceptive pill or a condom breaking. It is common in Australia to use the progestogen-only method. This entails a dosage of EC pills containing progestogen or the synthetic version. A doctor can prescribe the pill or they can be bought over the counter at a pharmacy without a prescription. Emergency contraceptionis 85 per cent effective in reducing the risk of pregnancy.

Sterilisation

Sterilisation is a permanent form of contraception. For women there are two types of sterilisation: tubal ligation, in which clips are placed on the fallopian tubes, or tubal occlusion in which a device is inserted into the tubes. These methods work by preventing the sperm from reaching the egg. Tubal litigation is 99.5 per cent effective. The Vasectomy (for men) works by cutting and blocking the tubes called the vas deferens, preventing sperm from leaving the testicles. The chances of impregnation with a vasectomy are 1 in 1000.

3. Extreme diet or exercising.

Making big changes to your diet or workout regime can often affect the frequency of your period.

“ Extreme exercise and diet can change your cycle by affecting your hormones and making your body think that you are in a life threatening situation with extreme weight loss,” explains Dr Fielder.

As a result, your body responds by shutting down unnecessary function and prevents you from reproducing.

4. Stress.

We already know the many ways stress can affect your health, but it could also be a factor behind your period being out of whack.

In much the same way as extreme dieting or exercise, stress can affect your hormones and menstruation by sending your body into its ‘fight or flight’ response, sending a signal to your brain to stop ovulating.

5. A sign of something bigger.

In some cases, an irregular or absent period could be the sign of a more serious condition, such as Polycystic Ovary Syndrome (PCOS), a medical condition that causes tiny cysts to form on ovaries.

"PCOS is a complex condition that results in infrequent menstruation and other signs such as excess in male hormone that can cause changes in your voice, skin with acne and excessive hair growth," says Dr Fielder.

Health conditions like sexually transmitted diseases, thyroid disorders, endometriosis and diabetes can also cause irregular periods, so it's best advised to see your doctor to diagnose or rule these out.

6. Age.

According to Dr Fielder, it's not uncommon for your cycle to change simply because you're getting older.

"In adolescent years when menstruation first commences it is very common for it to be irregular - something that happens again at the other end of the spectrum in the perimenopausal years," she says.

It's around the age of 48 and older that you could see your periods change in frequency and duration as you approach menopause.

If you're concerned about your menstrual cycle, it's always best to consult your doctor to pinpoint what's going on.

How do you deal with irregular periods?