Hello,
Pregnancy occurs only during the time of ovulation which usually occurs regularly, around day 14 of a 28-day menstrual cycle. It is seen that pregnancy only occurs if intercourse occurs within the 6 days prior to and including ovulation. If you had intercourse close to ovulation, then you can have pregnancy. Check out your last menstrual and ovulation date. Further confirmation can be done with paternity testing.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Sperm can live for almost a week inside the human body before dying. Even if the swimmer survived 7 days after the 16th that is only the 23rd. That's cutting it close and those conception dates could be wrong, so the best way to know 100% is to have a paternity test done.
However, because that is the latest it could theoretically survive (and it probably didn't survive that long), and the condom didn't obviously break, and the conception dating isn't usually more than a week off it makes the ex less likely. Especially because your current boyfriend and you had unprotected sex during the believed time of conception. Honestly I think you can be confident in assuming the father is your current boyfriend, but if you have doubts a parental test after the baby is born is the best option.