I've been using nuristrate for two months now , i was due for injection 3days back i had unprotected sex. can i be pregnant?

Maybe not, but...: Contraceptive protection doesn't suddenly vanish 3 days after a next contraceptive shot is due. That said, sometimes it can be hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. If worried, know that a urine pregnancy test gives a reliable result about 3 weeks after sex (3 weeks after when conception might have occurred).