Also keep in mind that dates will change during pregnancy, and the first ones you get are the most reliable for dating the pregnancy by quite a long ways. When did you begin to sleep with the second guy?
Skye, if that "puts your conception date the week of the period," that actually makes sense because doctors begin the date count of pregnancy (8 weeks, 10 weeks, etc.) on the first day of bleeding of your last period, not on the day they guess conception happened. If a doctor told you that you are "x weeks pregnant," he or she was counting back to the presumed day 1 of your period, not to when you conceived.
The only time I slept with the second guy was October 21. Other than that it was the first guy. This was all unprotected. I'm just worried because with the early July due dates it should be guy #1 and that's what I was thinking for the first 19 weeks of my pregnancy. Then I went for the gender ultrasound and it was moved back to July 12 and that is the one my dr. is sticking with. July 12 could be either so for the past 10 weeks I've been going crazy.
Only early ultrasounds are reliable for dating purposes [the later in pregnancy they are, the wider the margin for error, since babies grow at different rates]. Besides that, if the only time you slept with the second guy was October 21 and you are taking from the changed due date that you might have ovulated on October 19 (a day when you had recently slept with your boyfriend), I don't actually see why you think October 19 "could be either." The egg only lasts for about 24-36 hours after ovulation, and then it disintegrates.
I had done a little research online and for a July 12 due date it said the probable date of ovulation was October 19 but possible dates of conception were October 15-23 so I was just really confused.
When was the July 12 date given to you in terms of the weeks duration of the pregnancy? If it was later than the 12th week, it could be a week off or more.