How To Calculate The Date Of Conception Based On Due Date?

Hi, I believe I am 14 wks and 2 days pregnant . I think my last period was November 20,2014 I had sex with someone on Nov.28,2014 & had sex with someone else December 6 and 11 who do you think my baby father is? Doctor say my due date is august 27,2015 I'm ashamed about this so please don't judge me