When I did the ultra sound, I was told I'm 12 weeks pregnant. My first day of my last menstrual is January 9-10. I had sex with two guys & I have no clue who the baby father is, the first guy I had sex with was in December 28, 2016. And the second guy I had Sex with was in January 6, 2017. Please help me find out who the baby father day is because I am so confused to how to find out the conception date, and how the first trimester begins on your first period day and also how the sperm can live inside of you for 5 days so please help me because I am confused. Is the father the first or second guy?