My period started somewhere around the 10th or 12th of August and is not always regular but may be off a day or two.. I had sex with guy A on the 16th of August when my menstrual lightened. No condom but he did not ejaculate in me at all. My menstrual started up again the same day and lasted another 2 days- going off on Tuesday the 18th. I had sex with guy B on the 20th of August and numerous times a day for the next 4 days until the 24th of August (this is my boyfriend, no condom and he did ejaculate in me, every time). My ob-gyn is telling my i conceived on the 12th of August, before I had sex with either... while still on my cycle. HELP! I want my boyfriend to be the father.