What is causing my constant periods?

I am 19 years old and for about 2 years now I have suffered with constant periods. And when I say constant I mean I get about 1-2 days off before the next one starts. So my periods are lasting just short of a month. At first it was light and brown coloured but now its heavy and red and very painful. I never had pain before and I would be regular and had short periods that were the same every month. 2 years ago I started getting ill and was then diagnosed with mitochondrial disease. I'm not sure whether it has anything to do with it as the disease is so rare its hard to find out. However I feel like my illness is the primary cause of my period problems (my illness is basically where the cells in my body do not create enough energy, therefore I have muscle wastage and pain and weakness etc..) I was on the depo injection for a year and a half, then I went on the pill for a few months then I stopped all contraceptive to see if that would make a difference but the bleeding continued. I'm currently on a different type of pill and that still hasn't helped. I've seen 7 health care professionals, had internal exams and scans and ultrasounds and no one can find out why its happening. The only time the bleeding stopped was when I was prescribed norethisterone which stops your period short term. However I am no longer allowed this because there is risk of blood clot in my family. I would do anything just to have a break from this bleeding!! please someone help!