Heavy Periods in 16 year old?

I am 16 years old and has had my period for 3 years know. My periods are very irregular (usually once every 2-3 months). My periods are so heavy i have to change my tampon and pad every 45 min. I also was diagnosed with irritable bowel syndrome. Should I be concerned? How do i stop the heavy bleeding? Does taking a fiber supplement help my heavy periods? What should i do?