Re: Ok so my question for everyone is this--
Ovulation date is usually calculated by going back 14 days from the date your period is due. You didn't say in your post when your period was due, so it's really hard to guess which guy could be the father.
But since your doc told you you probably conceived May 1-5th and guy #2 is closer to that time, that would make him the more likely candidate.
Also, if you had sex a few hours before your period started (guys #1), it's very unlikely that that was implantation bleeding (that takes a few days).
All that said though, it is a very tricky one!
Ultrasounds are usually very very accurate in telling you exactly how old the foetus is. Have you had an ultrasound?