I would ask for a referral to a fertility specialist for further testing. It may well turn out to be 'unexplained infertility' or you may fall pregnant before needing any intervention, but it's worth getting checked out. There are so many things that could be preventing you from falling pregnant and an FS will know what to look for better than a GP or even an OB/GYN.
In the meantime I would look at doing a BBT chart to get a bit more familiar with your cycles. Google "Fertility Friend Charting" if you haven't charted before and want to know how it works.