Hi, you said "I got my positive test on May 8," did you mean a positive home pregnancy test in the morning on May 8? Or did you get a blood test?
These incidents were too close together to give a certain answer. Yes, the most likely date for ovulation was April 29th, but the egg is good for one day and the chance of you having an exact model cycle is not guaranteed. If you want probabilities, your ex "J" made a good deposit with almost perfect timing, while the co-worker pulled out and might have been a day late. My estimate is ten to one in favor of "J", but if you want peace of mind a paternity test after the birth would be cool.