Periods post baby

Hi mums,
This may be a massive case of TMI. Sorry in advance.
I had my 3rd bub in January. All 3 kids were csections, i bled lightly post birth for 4-8 weeks each time.
My bub is fully breastfed since birth (fed on demand day and night) but my period returned 4 months postpartum.
Ive never had period pain or heavy periods before.
But each month since my period returned its been an excruciating experience.
I bleed for over 8 days, and the first 4 days im soaking through overnight and maternity pads every hour.
Its like a tap.
No clots, just blood.
I sit on the loo and it just pours out non stop.
In the first 2 days i cramp so bad i can hardly walk- like think equal to posterior labout pain.
And if there is any movement in my bowel like wind or a stool, im doubled over in agony as it passes through, feeling like im tearing on the inside. I was walking down the hall at work this week on day 1 when i felt the tearing pain and i just dropped to my knees. I feel it before i even get the feeling of needing to poo or pass wind.

Id like to say at this point that i handle pain well. I live in chronic pain, i had an emergency csection that i felt them cutting me because there was no time to waste, and i didnt scream, i just told them calmly 'i can feel everything you're doing'.
Im no sook.

This monthly issue didnt happen with my older 2.

I have had PCOS in the past but that resolved with weight loss. This pain is different.

I don't have retained product- scans are clear.

Im not prepared to go on hormone therapy of any sort (aka the pill or iud or the rod etc) as it makes me horribly unwell in other ways.

Ive also been cleared od STD's, STI's and pap test is clear.

Im 32 if it matters.

Please help me shed some light on this.