Just a heads up, if your butt sores go away on a gluten free diet, you would need to go back to eating gluten for a period of weeks or months if you want to get formally tested for celiac disease. Otherwise, the testing will be invalidated.
https://www.drugs.com/inactive/sodium-starch-glycolate-128.html
https://celiac.org/gluten-free-living/gluten-in-medicine-vitamins-and-supplements/
Santina, are you a super sensitive celiac? If there is gluten in the starch used in this med it would be a very small amount since gluten is the protein component of wheat, not the starchy part. You can never completely separate the two but the starch should have only a trace of gluten I would think. It is also possible that you reacting to the active component of the medication itself.
It wasn't generic. I guess with that ingredient they use corn rice or wheat as a binder. Thats where gluten comes in. Like anything else hidden gluten!