I had sex with my boyfriend and he ejaculated in me and the next day I started to bleed. I've been bleeding for 3 days now. I'm 17 and I have been taking birth control pills for about 5 months now. My last period was about a week and a half ago, so I don't think it is that. I am worried I'm pregnant and it is implantation bleeding. Or could it just be from the sex? Please help.