What Is The Treatment For Irregular Periods?

Hi I'm 18 years old and my period has been irregular from the start when I was 11. I started keeping close track of it in 2009 and that year I had it 8 times, 2010 I had it only 4 times, and now I go anywhere from 1 to 5 months without it. When I get it it is extremely heavy and I get horrible cramps that prevent me from going to work and school. Lately a new symptom has come up. I have severe pain when inserting and removing regular tampons, but not every time. Why does this happen? I am engaged and my fiance is wondering if these problems are going to lead to infertility or difficulty conceiving.