conception

Ok.. i am confused. i had sex with my ex boyfriend august 1 and he climaxed inside of me. i then had sex with him again august 5th but he did not climax at all. we then broke up and i then slept with my now husband august 7 and he climaxed inside of me. we also did it on the 8, 9, 10, and then on. i took a pregnancy test and found out i was pregnant september i think the 12 when my cycle did not come. i was told by my doctor that my baby would be due may 16th 2010. who do you think fathered my son? the start of my last cycle though was august 9th.