I'm 12 weeks pregnant, I had sex with this guy on the 12th of aug and the other guy the 29th of aug. I want to know who could be my baby's father?

Since the dates of intercourse are so close together you will have to wait until the baby is born to have a DNA test done.

I agree with the last answer, the dates are so close together that the only way you could tell who the father is to have them take a DNA test so you can be sure who is exactly the father.
Congrats on the pregnancy. Best wishes to you and the baby :-)