Why do I have irregular periods?
When you first start to menstruate, you can have very irregular periods; starting, stopping and starting again. You could have one period and then wait as long as six months for the next one! This isn't unusual. Until your body adjusts to your menstural cycle, your period may be unpredictable, so please don't worry.
Having an irregular menstrual cycle is very normal during the first year or two after you start menstruating as it can take up to two years for hormones to settle down enough to make them regular.
I suggest you keep a menstrual/period calendar and record each period, including your flow pattern. If you are at all concerned, see your Doctor and take the calendar in with you to explain your irregular periods.