Im currently 36wks pregnant. EDD is June 14th. On Oct 8th I found out I was pregnant. My doc says I concieved?

give or take a few days from the 22nd of Sept. Well my current boyfriend & I had sex on the 22nd of Sept & on...but that week before I had been with someone else. Is the boyfriend now the father, like did it happen that fast? Gettin closer to having this baby & Im finding myself confused. My LPM is Sept 7th.