I am due April 15, 2008. I am not positive about when my last period was. On Aug 22, I went in for an early US which concluded that I was 6 wks, 1 day. Doctor gave me a conception date of July 23 or 24. My question is, I was having marital problems before all this and slept with someone else on July 16 but used a condom. What are the chances that he is the father? I slept with my husband the same day and days after that without a condom. Someone told me that having the same persons sperm inside you on a regular basis builds up a resistance to any other sperm, considering that sperm foreign. Please help....Please tell me its my husbands.