How old are you? In the States its recommended you see a doctor after 6 months of actively TTC if you are in your mid-30s, and after a year if you are in your 20's, early 30's. If you chart your BBT and have charts you can bring to your appointment or have some underlining condition such as PCOS that you are aware of, you can usually see a doctor even earlier.
Do you chart your BBT? If you don't, you should. It will show if you are ovulating or not. It's possible that there is nothing wrong and that you are simply missing your peak fertile days. Do you use OPK's? Do you have periods? Are your cycles long or extremely short?
I would begin charting if I were you, and would schedule an appointment ASAP. Not trying to scare you dear, but the sooner you go, the sooner you will hopefully know if there is something wrong or not.