What Causes Irregular Menstruation With Severe Abdominal Cramps?

I have always had irregular periods since when i first got them till now and that is going onto 11 years, however everytime i ask my doctor about it, she says its my weight, or its something else. I get them 3 - 4 times a month, for 2 -3 days or I wont get them at all, and this month I have had them for 13 days straight, and in so much pain from it. Im usually in pain from it when i do get them, like sometimes i faint, sweat a lot, take pain killers they dont work. My cousin has told me to get a test done on my ovaries.

please help me cause i'm worried about it =(