25yrs last period was january 24-29 i'm usually regular 27 to 28 day cycles. i still haven't started i was suppose to on feb. 20. haven't had any sex.

Not to worry: Even if you've usually been regular, it's not too strange to vary once in a while - especially if you're perhaps dealing w/ a cold or some other stress - even minimal. If you are concerned, contact your OBGYN or Dr for an exam. No sex would remove the question of pregnancy - you're right. I hope it's a simple thing and you are back on track soon.