15 days of cramps a month

hello ladies,

For as long as I can remember I have had painful periods with awful cramps. In my teens it used to be just a day before and the first 2 days of my period that I would get these cramps. For the last 5/6 months ( I am 30 ) I have had severe cramps for 10 days before my period and throughout my whole period. I am taking a box of midol every month. My doctor doesn't seem to think anything is wrong but I know something isn't right. Any advice???