Help!!

My boyfriend and I have been having unprotected sex, not really trying to get pregnant, but not really not try at the same time.. I've calculated and if I were to be pregnant, I'd be about 4 weeks this coming week.. I've been feeling kind of blah the past week, been cramping, sore boobs, and just having general aches in my back and abdomen. We had sex today, the first time since the 25th, and I bled during intercourse. We stopped because my boyfriend freaked out thinking he had hurt me. I wasn't hurting, cramping or anything, and after we stopped, so did the bleeding. Could this be an early sign of pregnancy? My period isn't due till the 4th, and It's always on time.