Have you tried going completely gluten free for 2-3 months? And that includes any derivatives that are often found in packaged products, condiments etc. Do you keep a food and drink diary to help find possible correlations between flare-ups and diet?
Have you checked for any food sensitivities or allergies? How about any malabsorption issues, e.g. SIBO, Candida, EPI, Chrohn's, celiac's?
And another area that is often overlooked is the sheer amount of carbs that are in the diet, which can cause systemic inflammation, pain, swelling, glycation of cells, oxidative stress, etc. Have you calculated how many daily carbs you are consuming? Have you tried getting into nutritional ketosis (0.5-3 mmol/L) and checked your A1c level to be 5.2% or lower?
Have you had a urine metabolite test done, such as the Genova FMV ONE or similar? Any nutrient deficiency testing been done?
Back pain is often a signal for issues that are not necessarily spine related. (In my case it was pancreas damage.)
Do you have a fibro specialist near you?