I became pregnant during July according to my due date of April 3 2012 my 12 weeks us said I was right on for the due date as well. Well my question is if I had sex on day 21 of a 30 day cycle in June could I have became pregnant then? I had a pregnancy test on June 28 (first day of period)which was negative and I had bleeding that continued for 6 days. This most likely sounds dumb but I just need to know for peace of mind. I had sex with someone else besides my current boyfriend and wouldn't want to be wrong when it comes to the birth.

I'm sorry, but in the end a DNA test will need to be done to determine paternity.

Yes it could be either man, you will have to wait till the baby is born and do a DNA test to know.