AM I Pregnant? Please someone answer this question!?

My boyfriend and I had unprotected (my first time) last night. It is now 17 hours later, and my period has just started. I HAVE HEARD of some women, such as my mother, having periods while pregnant. I do want to be pregnant, so Im trying to be as objective as possible. Is it possible that I am pregnant? I did not bleed anywhere near as heavy as I usually do, and that makes me a little hopeful. Being that it was the night before my period was supposed to start, am I just shedding the egg? Or is it still in the process of fertilization? Doesnt it take 72 hours?