Young and healthy.. Don't understand why we can't conceive.

Madeleine
I'm 22 my husband (24) and I have been trying for 14 months now to have children. The first six months we weren't too worried. Now I've pinpointed when I ovulate and we have tried several months now on that same day or some months a day before. What could it be? Any tips or advice? 
I have seen a docter. He told me I was "as fit as a fiddle" he could not find any reason why I couldn't conceive. It wasn't very helpful. 
Thank you ladies! :)