What do you think could be causing my irregularity?

Patient: I am almost 16 years old and have had my period for 4 years now. I have had irregular periods since the beginning and they have always been super heavy with lots of cramping. Before I started going to my Gyn, I was having three periods a month. The doctor made the decision to put me on birth control. They started really low because I have a family history of breast and ovarian cancer but because it was showing no results they have increased the dose. Still no results from that. Next they put me on an actual birth control pill as opposed to the low dose and I am still getting periods twice a month. I had an abdominal sonogram and it showed that I didn’t have cysts or endometriosis and Im not sure what to do now. They can’t figure out what is wrong with my periods and it makes me feel almost physically sick when im on them because my cramping is so strong. Do you have any suggestions of things that could be wrong with me that are causing this?