It is normal to have irregular periods for the first few years of menstruating — and sometimes even longer. But the only way to know if everything's OK is to visit your doctor or nurse practitioner . The length of a menstrual cycle can vary from girl to girl, but on average they're usually between 21 and 35 days.

What is the reason for irregular periods?

Sometimes, irregular periods can be caused by some medicines, exercising too much, having a very low or high body weight, or not eating enough calories. Hormone imbalances can also cause irregular periods. For example, thyroid hormone levels that are too low or too high can cause problems with periods.

What's considered an inconsistent period?

You have irregular periods if the length of your menstrual cycle (the gap between your periods starting) keeps changing. Your periods may come early or late. The average menstrual cycle lasts 28 days, although it's normal for it to be a bit shorter or longer than this.