Do you have any information from an early ultrasound? In other words, did you have an ultrasound in your seventh week or so, and if you did, what due date did they give you from that ultrasound? At this point, knowing you are 30 weeks is not as helpful as knowing what they thought the due date was when you were 7 weeks, if you got that due date from an ultrasound and not just from when your last period was.
It all depends on ovulation. But if you said if you had sex the day after your period it seems the second guy but it all depends when exactly and ovulation because sperm can stay there three days
It all depends on when you ovulated. Ovulation usually occurs on CD 14. So whomever it was about 2 wks after your period is most likely to be the father. Also keep in mind that doctors usually count pregnancy from 1st day of your last period, but the actual conception date is about 2 weeks later, so actual pregnancy would be 28 wks for you.