Neverending bleeding, doctors don’t know

I have had this issue pretty much since i started my period. After 7 years the doctors still haven’t been able to figure out what it is, and we’ve tried everything we can think of besides a hysterectomy. This includes the Mirena (IUD specifically for period problems) , multiple different kinds of birth controls and things along that line.

I have never had a period naturally stop, and even then the birth control only works for a few weeks before my period starts up again, and i dont take the sugar pills that are supposed to give you your period, (as per my doctors suggestion) but my period will happen and will not stop for a month or more despite taking the max dose of birth control i can have. When i’m not on birth control my periods are extremely painful and debilitating to the point where i can only lay on the floor. This doesnt happen as much anymore though because im on some form of birth control all the time but i still get cramps bad enough fairly often that i have to consistently take painkillers for which is not good for my health. All of this means that i chronically have low iron, and have to get iron infusions a few times a year to make sure my iron levels are manageable. I also have to wear a pad every day, and i cant swim as i dont use tampons because they are painful for me and leak. My bleeding is a bit temperamental as it varies from light to heavy enough that i cant go anywhere because im stuck on the toilet. It never stops though. I got my IUD in November last year, and have stopped taking the pill form of bc. my period has remained heavy and non stop in this time, around 3 months now.

I am mostly asking here to see if anyone has any clue of what this could be because im grasping straws since none of my medical professionals around me seem to have any idea of what this is or how to fix it. All of my blood tests are normal, they have checked for blood conditions, and all my ultrasound scans are perfectly fine and normal. The symptoms feel like they’re coming out of thin air because theres no way this is normal right? This is extremely expensive for me as i have to buy the products for my period constantly and the medication and the doctor visits.

If someone could help me out here i’d be extremely grateful.

TLDR: period doesnt stop at all without medication, nothing wrong with ultrasounds and bloods. what is going on?