I agree, also might try some opks. You may not be ovulating. Maybe you are and it's just taking some time. You may not have o'd for the 1st cycle or so and then started oing later, too. Good luck :)
I think you should chart your basal body temperature. If you google it, there is tons of info on how to do it and charts you can print off. It will give you an indication of whether or not you are ovulating and help time your intercourse. Save them every, and if you decide you need to see a dr, take them with you. Best of luck to you.