My due date is on the round the 22nd... its the 25th today and I'm very stressed... me and my boyfriend had sex sat,sunday(midnight) and Monday morning... he says he didn't in me... I get very light period cramps but no bleeding... should I b worried?

Yes of course you might be pregnant, or you might not... but the 'withdrawal method' is no method at all. Women get pregnant doing that all the time. Get some real birth control.

Of course, since it is possible you are pregnant.
You had sex with no protection.
First boyfriend says?? You would have seen where he did go, if it was not in you? On your leg? In his hand? On the sheets, it should be fairly obvious.

Next even if not "in your" there are plenty of sperm in the early fluids, to make you pregnant.