Pregnant? what's happening to me?

So sunday was my first day that I took my birth control pill after my period . I've been on BC for 2 years now. I took my first pill of the first week Sunday and had sex the same day and he came inside me. It is now a week later and I've been cramping, feeling dizzy and nauseous. Last night ( Saturday night) I had a party with some girlfriends and drank and got a little drunk. This morning which is a week from unprotected sex, I went to the restroom and I was bleeding really bad, this has never happened to me before, I've been cramping all day. Any idea of what may be happening?