i have had my period for 12 days bleeding heavy last 3 mo

I have had my period for 12 days for years. Everyone kept telling me it was a hormonal imbalance which I'm sure is part of it, but birth contol pills did not help my situation. I bled for 3 months straight one time and had to take birth control pills every 6 hrs. Even this did not work. I've been to many doctors. They finally diagnosed me with endmoetriosis a few years ago. I had surgery and my period went down to 9 days for 2 months but after that its back to same old 12 days. The only thing I can tell you is that you need to see the Dr., but in some cases even doctors cant help.