I responded to your post on the Crohn's board, but yes Celiac can cause severe joint pain, muscle pain and a host of other issues, it is also considered an AI disease. It can be mis-diagnosed and is hard to diagnose.
Biopsy and blood work are the best, but sometimes even that can't always give a firm diagnosis (in a small %). Sometimes you just have to cut out the gluten and see what happens.
See my post on the Crohn's board and I hope it helps some.
I have to admit, I never heard of Fleets giving the ulcers, but then I am not a dr. :) I am curious enough to google and might post on the Crohn's board about it, that is the only prep I can handle for a colonoscopy, and I have to have them pretty often. :)
I hope you get some answers soon.