My boyfriend and I had unprotected sex for the first time on Nov 8th and he came a little bit inside of me. I am on birth control and at the time haven't missed any pills. I had my period a couple days after the unprotected sex. And then I had my period again in December and I am expecting to have my period in 2 days. I've been having headaches a lot, feeling nauseous off and on for about a month but I haven't thrown up, I've been feeling lightheaded and I've been having what it seems to feel like constipation issues. Ive been extremely careful since that night he came in me, I've used condoms since then. Is there anyway I could be pregnant? Even if I've had my periods?? Why do I feel nauseous?