I'm sorry to hear that you haven't found any good answers to your symptoms over the last few years. It does sound like one of the problems is that you have been seeing a different doctor each time, which prevents the doctor from getting to know your case and working with you over several visits to get to the bottom of things. So that would actually be my first and most important suggestion, that you try to get set up with a primary care doctor
(who could be a family doctor
, an internal medicine doctor
, or an ob-gyn doctor) who could see you regularly, familiarize themselves with your case, and help guide you through this process!
I can think of several common ob-gyn conditions which could give some of the symptoms you are describing, such as irregular, heavy periods and abdominal/pelvic pain. These include polycystic ovarian syndrome as well as endometriosis. Please speak to your doctor.
The observation about starting your menstrual period after anal sex is interested. There is no physiological mechanism by which anal sex could trigger menstruation, and so this might be a coincidence of timing (for example, you had intercourse when your period was going to start anyway). It would also be important to confirm (as you might have already) that the bleeding is vaginal and not from anal irritation.