Thanks for consulting at my virtual clinic. I have carefully worked through your case, and I can realize your health worries. Being your physician, I assure you not to worry as I will take care all of your medical concerns. A women only gets pregnant when the sperm enters the egg and the fertilized egg gets embedded in the uterus. So in order to find the paternity of the baby through the following method 1) you can be impregnated only when a guy ejaculates inside you during your fertile period which will be roughly between 8th to 19th day from the beginning of your bleeding for a women with regular 28 day cycle. So check when you had sex with both. 2) When the baby is born from the blood group of the baby and the blood group of the mother the father can be identified. 3) In advanced cases the paternity can be identified through genetic tests The chance of impregnation without ejaculating inside the vagina is just a very rare. some times during intercourse ejaculation happens unknown to both man and women so it is hard to tell if the other guy NEVER ejaculated. But the chance of the other guy to be the father is very slim. Hope it helps. If you need further, detailed and quick assistance related to any health issues in future, feel free to ask me a question directly from my profile. Have a wonderful time ahead. Best Regards! Dr. Arunmozhi varman