I had sex on July 8th. I had sex again on two weeks later on July 22nd, but with a different partner. My due date is 04/18/14. Can you tell me when I conceived to determine the baby's father?

The only way to determine paternity is through a DNA test after the baby is born.

The date for sex is too close, conception dates are estimates and are not exact. So at this point, you will have to wait till child is born and do a DNA test

Did you have a period in the mean time?