What Causes Irregular Heavy Periods And Breast Pain?

I started my last period april 28 very light. the next day it was extremly heavy about every 50min would need to change . the next day nothing. Two weeks later I have had tender breast.. I never have tender breast. Im not do for my period to start till about may 25. My periods always last at least 5 days. The day my period was heavy the doctors had me take a p test it was negative. What would be the cause of this? Should I be worried?