How To Regularize My Menses?

I started my period 4 years ago and have never had a regular one. I get my period once every 2 months. I saw my GP 2 years ago and he asked me to come back in a year if it still wasn't regular. It's now 2 years on and I haven't yet been nor has my period become regular. Is there anything that could be causing this and is it worth seeing my GP again?