@elmay - I have been through similar misery. I had been suffering with a then undiagnosed gastrointestinal autoimmune illness. Part of this was Sjögren like symptoms- mouth and eyes- but tested negative a couple of times. I had painful blisters inside the lips and cheeks and red, sore tongue with Superficial ulceration. Flared up when my GI tract did. My doctors at Mayo assumes it was an autoimmune expression of the GI disease. I used all possible products to keep the mouth moist. My teeth deteriorated because of lack of saliva.
I was eventually treated with immunosuppressive medication for my GI illness. A while after finishing the treatment I noticed the dryness gone. Actually drooling.
I think you could get a second opinion about treatment of your mouth. I’m sure there is a way to be more comfortable. If you live near a major university hospital, check to see if any of their departments mention treatment of Sjögren’s.