I do realize that I made a mistake I said I finished my period December 13th when indeed it was November 13th - my appologies. Thank you all for all of your comments they have helped me greatly.
Plan to have an ultrasound at around the 7-weeks point, meaning 7 weeks after the first day of your last period. Then ask the ultrasound tech when conception might have been, based on the crown-to-rump measurement of the embryo. This kind of dating is not too reliable later in the pregnancy (since embryos and fetuses grow at different rates) but it is pretty reliable in early pregnancy. (Nothing much can be seen in the fifth week after your period, and the sixth week is iffy, but something can be seen in the seventh week.) Be sure the tech understands you want to know when conception was, not "how far along" you are, because she might give you a count based on the first day of your last period if you are not specific in your question. This won't rule out anyone but might give you a little help.
Oh goodness, how sticky this is! Suggestion only: First get an estimated date of conception, see if it matches up with any one man. Next, I have found, trully, that honesty in my life always provides the most relief and makes me feel the best about myself and is fairest for all involved. Keep in mind you have a couple months to do this. If the estimated date of conception comes close to any man, speak to him first and tell him you might be having his child, but you're not sure. If there's any man that's a keeper here, I would also tell him you're expecting and there's a chance it may be his child. It might not hurt to telll your ex as you have a raptore with him. Man1, unless test dates match up, keep his contact info! Perhaps tell him you may be pregnant, but you'll let him know. EDOC should be able to rule in/out man1. Go through you're pregnancy, enjoy, leave it up to the men for whatever they want to do-it's not your problem, and first date you can, get genetic testing. That's just a futeristic scenario, but I always like to live in the moment, day by day, and follow my heart, so that's what I suggest for you :)
If you had a period that ended December 13, why are you worried about sex before December? It sounds like you are saying that you had the period after the sex.
If you are saying you finished your period November 13, then it could be any of the men. Even the first guy is possible, since sperm lasts 5 days in your system. (By the averages, the second man is a tiny bit more likely to be the dad, but with PCOS you can ovulate pretty much at any time.) If you are keeping the baby, you will need to do a DNA test when the baby is born to be certain. It's only fair to the baby and to the father too.
The only way to know for sure who the father is, is to get a paternity test done. POS makes it harder to get pregnant, but it is never impossible for it to happen. You can try to guess who is the father based on your due date, but you won't know for sure until you get a paternity test done.