31 and never been pregnant...Ever!

I don't understand why I've never gotten pregnant! I'm 31 years old and have been with my bf for 3 years now. He has 3 children from a previous relationship so it's definitely me who's having trouble. A little background on me....Doctor has told me in the past that my cervix points downward (Don't know if that has anything to do with making it harder to conceive) and also have had precancerous cells on my cervix cut off 2 different times. It's frustrating and depressing. Any suggestions on what might help?