My ob said i conceived on sept 8 my lmp was aug 26 & having normal periods every month. had sex with 2 men, 1 a day before my pd, and 1 after. father?

Confused?: If you know your conception date (which agrees with your last menstrual period date), then are you asking if you got pregnant by 2 different men that you had sex with on 2 consecutive days? If that's your question, then then answer is: it would be impossible to say who's the father without a paternity test. If that's not your question, consider rephrasing your question.

My best guess...: In the setting of regular cycles, and based on a LMP of 8/26 and assuming that an early ultrasound confirmed your due date based on the LMP dating, then the most likely date of conception was right around 9/8. I cannot give you a more accurate answer without the results of an early ultrasound.