Can my conception date be wrong?

Right now I almost 6 months pregnant positive pregnancy test on January 29, 2012. My last period was December 22, 2011 (that was the first day of my period). According to my LMP I ovulated on January 5, 2012 and implantation happened January 14, 2012 and due date would be September 27, 2012 Expected period January 19, 2012. I had UNPROTECTED sex with guy #1 (about 2-3 times a day) from January 6-8, and PROTECTED (he changed the condom 3 times during sex, none broke or tore) sex with guy #2 on January 14th and it was only one time and he came in the condom. I had my first ultrasound February 18th (going by my LMP I was 8w 2d. It was not a trans-vaginal ultrasound but a regular over the stomach ultrasound) the tech wouldn't tell me how big the baby was measuring an said my doctor will tell me at my next appointment. When I had the ultrasound she had to push on my stomach a little hard to get an image of the baby. On my doctors appointment he said the baby was measuring 7w so my due date changed to October 7, 2012, ovulation January 15th, Implantation January 24th, and expected period January 29. My question is who could be the father? My strong guess is the first guy because it was unprotected, and around my ovulation according to my LMP, and even though the ultrasound measured 7 weeks I've read that they can be wrong up to 5-7 days? I am getting a DNA test done when the baby is born I just want peoples guess who it might be.