maybe it could be his sperm count. i saaw on an episode of Dr. Phil the other day a couple who had been trying to concieve a second child for 2 years. they had a 3 year old daughter together. but when they went to see the specialist it turned out that 1 out of every 2 sperm either didnt have a head or a tail..thats why she wasnt getting pregnant.
check out women to women website. they have a listing of a non profit fertility agency. maybe they can be of assistance. have you used any ovulation kits?
well, i think, you should consult a fertility specialist since its 3 years now. they can run some test on you. to chek wht is going on with ur body. Good luck.