help!!

my fiance and I have tried for almost 2 years to have a baby and nothing got accomplished. he went to jail back in February. I messed up and had sex with a different guy march 17th and he got out march 22nd and we had sex every day after that. I found out I was pregnant April 10th. at my doctor apotiment I asked my doctor who the father could be.

My due date it December 22nd. please help me. when did I get conceived?...