Its my 4th day of menstrual cycle.i had unproeced sex.can I be pregnent?

As a rule, if you have sex without protection there's absolutely always a chance that you'll become pregnant. Even if he didn't ejaculate inside of you, men start releasing sperm pretty early on as they become aroused, even if just small amounts.

So to answer your question yes, there's a chance that you could be pregnant. But at the same time, I wouldn't advise you to start worrying until you know for sure.