Although it seems confusing to you, it's very common for young women, especially those who haven't been having periods for very long, to have gaps of several months between them. Older women can also sometimes find that their periods stop for a while.

There are many possible causes and it doesn't necessarily mean that you're either pregnant or never going to have another period and so be infertile. (These are the two main worries that women usually have when their periods stop - just for extra stress. They often worry about both at the same time which can blow your mind a bit!)

I'm not sure what tests your doctor has done but it's likely that they've ruled out anything worrying, and you'll probably find that your periods start again soon. If this doesn't happen, talk to your doctor again and ask them why.

Could you be pregnant?

Three negative pregnancy tests make being pregnant extremely unlikely (although this has been known to happen). If you're having unprotected sex then there's always an ongoing risk that you could become pregnant, and you should talk to your doctor about contraception.

Young women

Very few young women find that when they start their periods it all runs like clockwork from day one. Instead of a regular period at a regular time each month lasting a regular number of days, there's usually a month or two missed here or there, sometimes two periods in one month (which is a bit of a pain). After a year or two things settle down into a regular rhythm, but even then every woman misses the occasional period.

Some women find their periods go on being irregular. The most common cause is a condition called polycystic ovarian syndrome (PCOS) where hormone levels in the body go awry. This doesn't necessarily mean that these women will find it harder to have children, especially because these days there are effective treatments to help.

Medical reasons why periods stop

There are some medical reasons why periods can stop for a while or even for good. These include simple things which affect us all, such as stress, emotional upsets, travelling and general illness.

Extreme weight loss can also stop periods. If you lose more than ten per cent of what your normal body weight should be, the hormonal control of menstruation is upset. Your periods should return when you regain the weight but sometimes it takes several months for the normal cycle to start again.

Extreme exercise can also cause your periods to stop, usually because it's associated with weight loss below healthy normal levels needed for hormonal controls to work.

Very occasionally more serious medical conditions can interfere with periods. These include brain tumours in the pituitary gland - a gland in the brain which oversees hormonal controls in the body. Another rare problem is primary ovarian failure where the ovaries stop producing eggs for an unknown reason.

This article was last medically reviewed by Dr Trisha Macnair in August 2008