Based on your last period, your fertility window was most likely between December 22nd and January 1st. You could have ovulated anytime between those dates, as it is the most common time for ovulation to occur. Unless you know the exact date you ovulated, (there are ovulation tests you can take) there's no way to make an accurate guess. If you ovulated early in the window, then it could be the first guy. If you ovulated a few days later, it could be the second guy. I'm sorry, but I think you should speak with your doctor about a paternity test.