After sifting through all the possibilities - and then finally stopping the generic Plaquenil for a week, and restarting with brand name Plaquenil - my stomach problems vanished. So it appears that the pharmacy's switch to a different manufacturer of my generic plaquenil was the culprit afterall.
Unfortunately, it now costs me an extra 30 bucks a month. Both my rheumy and GP have said that when the pharmacy says the products are "identical" it's not literally true - that maybe the main ingredient is identical, but the fillers, binders, etc. are not - and they have many patients who have no trouble with one supplier, but can't take another manufacturer's. I'm still not sure whether the issue was gluten, and would have occurred with either of the generic manufacturer's (Brand Plaquenil is gluten free).....or something altogether different. Just glad to have my stomach back to normal.
Just thought I'd post in case others have similar problems.
diagnoses: mono 1972; postviral CFS 1997; fibro 1998; UCTD & osteoporosis 2007; celiac 2009
meds: Plaquenil 400 mg, occasional low dose xanax for sleep aid, artificial tears w/ ointment at night, Advil/aspirin prn and lots of vitamins