If there's any chance at all that it could be stress-related, please try Dan Buglio's videos on youtube, he's really gotten me out of trouble:
https://www.youtube.com/@PainFreeYou
I strongly believe that this is because most back pain, along with many other ailments such as IBS and migraines, are caused primarily by repressed stress/anxiety.
Would recommend to anyone to have a look at the info here: https://www.tmswiki.org/forum/
I have posted it before, but I went from...