Today I am 10 weeks 1 day pregnant. I had sex with a friend one night wich was September 16. My last period was September 15, than September 22nd & so on I had sex with my current boyfriend I found out I was 10 weeks 1 day by a vaginal ultra sound. When I count back 10 weeks 1 day I'm getting the date of when I slept with my friend. He didn't because we stopped having sex.. but what worries me is precum Anyway my due date is June 22nd. When I called my Doctor the nurse told me I conceived around sep 29th what I'm curious about, is how am I coming up with Sept 16th which is 10 weeks 1 day ago? Please help.

It isn't really possible to determine what day you conceived when you had sex that often around the actual conception day. The nurse probably just added 14 days to the first day of your LMP, which you say was Sept 15, because you are most fertile mid month. The odds of getting pregnant the second day of your period are low, but there is no such thing as 'never get pregnant' any day of the month.
Later ultrasounds might predict a little bit better, but NO ONE EVER can predict which of your sex partners is the father. You will have to get DNA testing done when the child is born. Maybe with the guy from the 15th, to rule him out, and not even mention it to your boyfriend.

Let me clear up one thing joypulv said. We, as nurses, don't "add" days to the LMP. There is a scientific calculation involved with calculating due dates. It's made easier with a current gestational wheel.

If your LMP was September 15, you most likely conceived on or around September 29. This according to my gestational wheel.

With that said, due dates are still an estimate as the calculations are based on the law of averages. You will still need to have a DNA test done to determine paternity.

And earlier ultrasounds are more accurate than later ultrasounds.

Oh okay, & oops I kind of told my boyfriend because I mean I'm so sure, my doctor told me I got pregnant the 29th so he said it was the 22nd that I did it w/ my boyfriend o:

Sperm can live inside a woman for around 5 days before conception occurs. But, in the end, you will still have to have a paternity test done. Again, this is all based on the law of averages. Not every woman falls within these averages.

All right thank you.