I got pregnant about a month before I left on a study abroad trip through my university. I am not positive who the father is but I believe it is my boyfriend's. I slept with someone else but we used a condom and we only had sex 1 time. My boyfriend and I were not using any birth control at the time. Is there any way I can determine that my boyfriend is the father? I used a conception calculator with my due date and the conception date it gave was during my period. Is it possible to get pregnant on your period?