Endo? Confused?

Long post, please stick with me!

So I've had issues with my periods for 7+ years now, I went on the pill at 15 to lessen the amount of bleeding but I was still in intense pain and would often have fainting spells alongside. Then a few years ago I had to change to the mini-pill as I was having migraines. I didn't have a period for 18 months of so and I was more than happy with that! Then they came back (been about a year now) no regular schedule, can last 3-4 weeks stop and then restart a week later of go 3 months with nothing. The blood itself is never red. It is always brown in the way a period is towards the end of a cycle and is this way through the whole period. I also get large clots which are incredibly painful to pass. Along with this for the week before my bowels and peeing are affected. I also have intense pain in my back, hips, stomach and pelvis. They become painfully urgent when I need to go and hurt very much so. I also get more dizzy and feel unwell while I'm on (I also have T1 diabetes, EDS, POTS and MCAS).

I've had some blood tests done, had a smear and about 6 months ago had an internal and external ultrasound which came back normal, just showing a few cysts on my ovaries but they said they were normal.

What could be wrong I'm at my wit's end now with being so unwell during such a long period of time?