My back pain story was set-up related.
Friend of mine suggested that I check-out my set-up. Turned out I was riding the wrong size frame (too small). On longer rides I would get a dull ache in the area around my kidneys.
So, I bought a larger frame, sorted out my set-up and no problems since.
A friend of mine had hurt himself almost to the point of having to give up cycling altogether.
I had to try quite hard to get him to change his set-up. Eventually he did though, (last-ditch attempt by him to stay on two wheels and he hated the new position at first )
But, it worked, and he still cycles today. He was so surprized that altering your position on the bike could help so much.
I'd start with looking at/checking that my set-up was good, before doing anything else.
Good luck, I hope you get the issue sorted soon, whatever it is.
🙂