I had sex with my bf about 5 weeks ago, and since then, I have been feeling nauseous. And just recently my boobs have started to feel a little tender. I have taken home pregnancy tests and have gone to the clinic to get a physical and pregnancy test, and they both say that im not pregnant. But I have watched those television shows about women not knowing there pregnant, so Im starting to wonder if there is something going on. I did have what I thought was a period a week after having sex with him, but then I thought that it could be implantation bleeding. I dont know if im overreacting, or if there is something going on that I should worry about.