Hi, if you have a regular period your baby would most likely be of the guy you were with on the 15. Good luck!!!

How long are your periods? If you normally have a cycle that is about 30 days, then the guy who was on the 15th is the more likely option. If your periods are irregular, or sometimes longer, then it is really up in the air. Even if your period is normally 30 days, you can never be fully sure that it'd be the 15th (if you are under stress it could have delayed ovulation). The only sure way to tell is to get a DNA test once the baby is born.