What Causes Irregular Periods With Severe Pain?

i am 28 years old 120 kgs and i suffer from a very irregular period since i was 13. i was molested at a young age and always put it down to that i have had blood tests and doctors cant find anything. some months i skip periods completely other months its normal and most of the time im in severe pain with periods where it goes down my legs and i cant move and get really hot and cold, these periods are severely heavy flow where nothing holds it and huge clots. once i bled for 3 months straight i know i should get it checked but all doctors just say some women have irregular periods is all this normal?