ditto the above. even if you have regular periods, if your hormone levels are a little off (for either of you) it can make it hard to get preg. Find a reproductive endocrinologist if you can...the testing is far more comprehensive than you would get from your obgyn.
As the other ladies said, see a doctor. We can only speculate as to why you are haivng issues. A doctor can tell you way better then us what you next steps would be. In all likelyhood you may not be ovulating at all...like me, despite and OPK saying I was going to. Or your hubs could have a very low sperm count...or no sperm. I mean there are a million little things that need to happen just so and perfectly for any woman to get pregnant. Hang in there and get yourself into a reproductive endocrinologist! Pronto!