Personally i would ask to be retested, 20 years is a long time and medicine has moved on with better diagnosis. You could just be sensitive to wheat/grains rather than coeliac but if you have concerns that it is this, you should ask for a referral. Many people take years to get a correct diagnosis, often brushed off as ibs.
You could do a food diary to see whether anything jumps up and says 'its me' causing symptoms. Fibro is in the auto immune category - along with many many others! Ask for b12,folate, vit d to be checked when you have bloods done, as for many those are out of kilter too.
Dont cut out gluten at this stage either because you will more than likely be told to go back on it for any tests, which for many can be intolerable.
I'm not an expert but I believe you can develop coeliac; I'm basing this purely on the fact that I had blood tests for 2 of the coeliac genes, and was positive for one. I had a biopsy 5 years ago which was negative but the letter I received informing me about the gene test results said that I could develop coeliac at a later date.
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