My husband and i are trying to conceive, but when we're done his come falls out of me. what can we do and why does that happen?

Normal: What you are describing is normal and won't prevent pregnancy. The vagina is a blind pouch and most of the seminal fluid that goes in will eventually come out. Sperm swim out of the seminal fluid into the cervical mucus and on into the uterus and tube, but the liquid they are in will need to come back out. You can prop yourself up on pillows for a 1/2 hour afterwards if you want to delay it.