I am so sorry you have such conflicting viewpoints from your doctors on your conditions. Hopefully, at least one of them will get to the bottom of the situation and diagnose you properly.
As for fibromyalgia, I suffer from that and I do mean suffer. While it is not an autoimmune disease, it sure takes its toll on me, I have to admit. I take oxycodone 15mg every four hours, just to keep the pain at bay and some times I find I have to take concurrent advil with it. No fun this fibro. But I have had it for over 30 years.
Please try to get an accurate diagnosis for your back though. As was already said, you could be doing yourself harm by not knowing. I have a back history as well.
I wish you luck. Keep us posted on your condition. I, personally, want to know how you are doing.
Co-Moderator Chronic Pain and Fibromyalgia Forums
Believe in yourself. Be kind to fellow humans and animals. Take time to smell the flowers and the coffee.
And by all means, when you are down, ask me for help. I will be there.