my boyfriend and I have been having unprotected sex for awhile now. I started my period about two weeks ago and we had sex while I was on it. and my bleeding lasted longer than normal. about a few days after I stopped bleeding we had sex and he came inside me. now it's been about 5-7 days since then and I'm having really bad cramps and kinda nausous but I don't throw up. what is causing this!?