i have been sexually active for awhile now, and me and my boyfriend have sex every now and then. Well about 12 days ago we had sex and since then I have been feeling the need to throw up. A few hours after we had sex i felt sick. I know that it's not a guilt thing, and this is the first time that i have felt sick after sex and it's not an std. I took a pregnancy test 6 days after we had sex and it came back negative. Any ideas?