I'm aged 13.5 years.

I had my menarche on 10th Feb and thereafter I had my periods on 28th feb and then 0n 16th march and again now on 29th march. Why is this so irregular.

Period generally lasts 3-4 days

Regards

Because you're still relatively young, your periods will be irregular, until your body sorts out its timing and release of hormones etc, periods can be 10 days apart or 50 days apart, sometimes you might even skin a period. It happens, though in time, your body starts to get it right and it will come to 28 days or thereabout for a complete cycle.

Hope this helps,
Louis.