This is going to sound really stupid, but I can't help it. My boyfriend and I were laying down, I had yoga pants and a thong on, and he pulled "it" out and got cum on the back of my pants. I washed it off when I got home a half and hour later. I'm on birth control too (have been for about 8 months). I've never had sex before either, if that means anything. And I'm slightly underweight. I'm just nervous. Any possibility?