My calculator suggests January 11 for conception. When you say one guy was in the beginning of January, could that have been as late as the 6th or 7th? Because sperm can live a while in your system. Was sex with him unprotected?
It is also significant if you got your due date from an early ultrasound or a different kind of estimate, such as counting forward on a calendar from the first day of your last period, or using a little wheel. An ultrasound in your first trimester is pretty much the only way to be able to try to figure out a conception date very specifically, other than doing a DNA test. If your estimated due date was told to you later in your pregnancy than your first trimester, then any estimated conception date based on it might have a pretty wide margin for error, forward or back.
Id definitely do a DNA test but probably the one in beginning of January. Im due 10/7 and my husband and I conceived around 01/09
Get a DNA test.otherwise you will always wonder since ovulation can take place at different times.
I would guess whoever you slept with closest to theend of your last period. Good luck.