Hi, namie, when you say "and next is Aug 17 which is my last period," are you simply saying that you had a period on August 17, or are you saying the next time you had sex with your boyfriend was August 17, or are you saying you had sex with the first guy on August 17?
If the last time you had sex with the guy who is not presently your boyfriend was June, he is most certainly not the father of your child. I see you saying on the pregnancy forum that you are afraid your boyfriend is worried because you had a prior relationship as recently as last June, but that would not make that earlier guy the father. He would be two months too early. And having a period in August is proof of that.
If your boyfriend is actively worried about this, get a DNA test done. They are not that expensive once the baby is born.
Namie, your numbers point to sex in August being responsible. How did you come up with 23 weeks pregnant, and when did you get that estimate.
Let me guess you had an ultrasound Jan 7th. Weeks 23 takes me back to last period Jul 30th, ovulation for this pregnancy Aug 13th. That does not put either guy as a possible father. An ultrasound this late could be off by several weeks. Backing up three weeks takes me to ovulation Jul 22nd with sex in the window Jul 17th thru Jul 23rd responsible. I can't imagine the ultrasound being off by more than that, so June sex is out of the question. if you did not have sex at any other times, the recent boyfriend is the more likely father.