I am 20 weeks pregnant. My husband and I are so excited. We are having a boy!

The month that I conceived my child, I was a mess, my marriage was shaky. My week of ovulation was November 12-17ish. I had many nights of unprotected sex that week.
As I said I was a mess, I also sex with another guy the 10th and the 22nd, before and after my ideal time to get pregnant. But we used protection.

My husband and I are so excited and so perfect right now. I just pray that it is his. I need some reassurance. HELP!

The ONLY way to find out who the father is would be a DNA test AFTER the birth.
Dates are merely best guess and there are too many variables to be accurate.

Yes you will need to do a DNA test when the child is born to be sure. No other way.