I went to my doctor after a year of trying and, as I was over 30, he was happy to refer me straight away for further investigations - had I been younger, i think that the guidelines are that you should be trying a bit longer first. I also had very irregular periods, and went on to have an internal scan, blood tests and also a laparoscopy - they said that one of my tubes was partially blocked but I was otherwise fine. Once they gave us both the all clear, I got pregnant straight away.
I would try not to stress too much, but go to your doctor or family planning clinic if you are concerned. Of course you are entitled to treatment if you need it.