I had my periods on 28th feb which ended on 4th march. in april it has not arrived yet. is there something to worry?

Need more info: There are a few common causes for being "late" with a period. If you usually have cycles very regularly (e.g. Every 28 days) and are now almost 3 weeks late, the first thing to get is a pregnancy test. If negative, then delayed ovulation may be the cause. These two account for the vast majority of late periods. Less common things can be tested for. Best to have your physician evaluate you.

Missed period: You have missed your next period. If you had unprotected sex, pregnancy would be the most common cause, check a pregnancy test. If negative, you may have a had an anovulatory cycle and wait for the next period to arrive. If the next period does not come, see a dr. For an evaluation. Good luck.