Hi and welcome to the board. The ladies on here are outstanding.
It really could be any number of things...Your tubes could be blocked, his count could be low... Clomid basically makes you ovulate...and if you are doing opk and getting + then you probably are already.
First they will have you do blood-work to check all your reproductive hormone levels. Then go from there. If all that is good (and depending on when the blood is drawn, they can tell if you are o'ing.) then they will move on...maybe HSG test. That is a test where the put die into your uterus to see if your tubes are blocked...
Sorry I could not be any more help...but