We just had our first daughter after a long hard fight against infertility. We started with my regular OB-GYN, who took me through some routine treatments like clomid. When I didn't respond to that, I was referred to an RE (fertility specialist), who proceeded with further diagnostic and treatment methods. We eventually underwent IVF to conceive, but there are many other methods that can be effective.
To answer your question though, you should discuss your efforts thus far with your OB-GYN and decide how to proceed. I don't know that most OB-GYN do much diagnostic testing, so your doctor may refer you on to a specialist.
I saw Dr. Le at Advanced Reproductive Care Center in Irving, and I don't have enough great things to say about him.