I had sex with someone nov 15th and someone in december, who is most likely to be the father? today i am 36 weeks and 4 days

Hard to guess: If it matters which is the real conception date, a woman must always separate her possible conception dates by at least 2 weeks... which means planning ahead every time. So, this may be too close to call. Life is never exact. Of course, the traditional method that has worked for thousands of years is, "The father is the man married to the woman." The modern way is DNA testing, if one wants to.