irregular menstruation?

I'm am an athletic 115lb 24 year old with extremely irregular periods. I was wondering how many other women there are that have the same issue. I am not on any birth control (haven't been for at least two years) and I only get my period every 2-3 months. The months that I don't menstruate I experience PMS as well as extremely tender breasts. How many of you are in the same boat as me? Should I be concerned?