Irregular Periods? A Doctor Reveals What the Causes Could Be

Periods can sometimes have a mind of their own. They can become infrequent, erratic and irregular for many reasons. Most of the time, there is no concerning underlying cause and they sort themselves out with time. But if you haven’t had a period for three to six months or if you miss a period and have associated symptoms like abdominal pain, you should visit your doctor to arrange the necessary tests to diagnose the reason.

In the meantime, I’ve plotted out some of the common reasons for missed or erratic periods. Sometimes it can be lifestyle-related, so checking in with yourself is key. Keep scrolling to find out more.

What causes missed periods?


If you miss a period, the first thing to rule out is pregnancy. If you a miss a period and have other symptoms like abdominal pain, spotting, dizziness, vomiting or feeling generally unwell, you should see your doctor who will assess you and arrange further tests to exclude miscarriage and ectopic pregnancy.

Polycystic Ovarian Syndrome (PCOS)

PCOS is a very common gynaecological problem that is caused by an imbalance of hormones. It causes multiple fluid-filled cysts to develop on the ovaries. These follicles are underdeveloped, which means that ovulation does not occur in a regular monthly cycle. Periods become irregular as a result. PCOS is characterised by other symptoms as well as irregular periods including:

  • Acne
  • Excessive hair growth
  • Obesity
  • Fertility problems

You can read more about PCOS here.


Starting, stopping or changing your form of contraception can also result in irregular periods.

The intrauterine system, like the Mirena coil, releases progesterone locally in the uterus, which commonly has the effect of stopping periods altogether. It is for this reason that the Mirena is an effective treatment for heavy, painful periods (menorrhagia). The copper coil, on the other hand, typically has the opposite effect and can make your periods slightly heavier and more painful, and therefore should not be advised for women who suffer from menorrhagia already.

The contraceptive pill works by suppressing ovulation by blocking your natural hormone cycle with a combination of synthetic oestrogen and progesterone. It can take time for your body to adapt to the new hormone combination, which can cause spotting or irregular periods. If you are sexually active, it is important to do a pregnancy test to be certain that you are not pregnant, as nothing is 100% even if you are using contraception.

Starting the progesterone-only pill (POP), classically causes irregular bleeding when you first start it, which can take up to three months to fully settle. If this occurs longer or you are developing other symptoms like tiredness or heavy periods, visit your doctor to arrange some tests and make sure this form of contraception is right for you.

Stopping any kind of hormonal contraception can also result in irregular periods or a delay in restarting your periods altogether. This is because it can take some time for your natural hormones to kick back in and restart your cycle after being suppressed by the hormonal contraceptive. If your periods fail to restart after six months of stopping your contraception visit your doctor.

Thyroid disorders

Your thyroid gland produces thyroxine, which a hormone that basically controls our bodies metabolism. If your thyroid gland becomes overactive or underactive, it also affects your hormonal balance controlling your reproductive system, which can make your periods irregular. Your GP will check your thyroid function tests as part of the full work up to diagnose the cause of your irregular periods. For more information, here is more information about thyroid symptoms.

Lifestyle factors

  • Extreme weight loss or weight gain
  • Stress
  • Excessive exercise

All these lifestyle factors affect the natural hormone balance of your reproductive system, which can result in missed or irregular periods.

Investigation and Treatment

It is important to realise the missed or irregular periods can happen without there being a serious underlying cause. But if you miss more than one period, your cycles become erratic or you start to bleed in between your periods or after sex, then these are signs that there may something else going on, and you should see your doctor. Your doctor will assess you and may decide to run some basic tests and arrange an ultrasound scan to investigate things further. In some cases, your doctor may go on to refer you to a gynaecologist for more specialist input.

Treatment ultimately depends on what the underlying cause is found to be.

Remember even the simplest of things like healthy diet, regular (but not excessive) exercise, less alcohol, no smoking, stress relief, early nights and relaxation are essential to our general health and keep our hormones in a balance, which in turn makes our periods more likely to be regular. Improving your lifestyle is a part of the treatment for PCOS and stress management, as it is the foundation for optimal physical and mental health and well-being.

Next up, these sobering photos show how endometriosis can drastically change your body.