Welcome to the forum.
Sounds like you've been through hell. Sorry you are in such pain.
Did your doc say why you were in such pain?
Has there been a diagnosis related to the extreme pain you are now experiencing?
I don't have any answers as to your pain levels and subsequent diagnosis, sorry. I think you probably need a comprehensive good workup from a good doctor - what about going to Functional Doctor? They operate a little differently from most doctors, who only see their little specialty, whereas the Functional Doctor is more of a "big picture" type doctor whose expertise can span several specialties.
But with your history of cancer, I would suggest you look into LDN, low dose naltrexone. It has helped many go in remission with UC and Crohns, but also is a cancer preventative. Actually it's also been used very successfully in the treatment of many stage 3, 4 cancers of all different types in conjunction with radiation and chemo.
If you like, feel free to email me and I will give you all the informational links and sites, as well as the how, and where info as well.
Good luck, and I hope you start to feel better soon.