Just dropping in to say I hope you feel better soon, that pain sounds unbearable.
My mum got lidocaine patches on nhs scotland. Don't know if that may be an option for you or if the heat patches you use contain the same active ingredient.
She also got oramorph. As in morphine she didn't notice much difference but I think it's because she didn't let it build up enough just wrote it off and stopped after a couple of isolated attempts.
I'd recommend acupuncture for anything if you can afford it. From an acupuncturist not a sports physio or something ie someone who does acupuncture for eight hours a day rather than occasionally.
I thought with my back pain that the problem is that everything gets inflamed when something in your back is out of place.
And then the inflamed bit and the inflamed place it's meant to go into don't marry up again.
So the inflammation needs to be reduced and it needs to be encouraged back in. And then you need to do exercises to keep it in by strengthening everything in the core up.
The bit I don't get is how they do they get it back in? A chiro will basically shove it back in if it's something small but once it gets too bulgy presumably they can't? Is that why we get encouraged to take exercise? In the hope it will slide back in?
People slag off chiros but in my experience they've helped me. Quickly. Before things got too swollen and wouldn't fit back where they should.
When I went the nhs route with physios and exercises the next time my back hurt it took for ever.
I know that's not helping you and your problem is different to mine just saying in passing that if it happened to me tomorrow god forbid, I'd be down the private chiropractor route not physio and it'd be the first available day.
I do hope you get relief soon. It sounds awful.