there could be wheat (among other things) in your xanthan gum!?!
Xanthan gum may be derived from a variety of source products that are themselves common allergens, such as corn, wheat, dairy, or soy. As such, persons with known sensitivities or allergies to food products are advised to avoid foods including generic xanthan gum or first determine the source for the xanthan gum before consuming the food.
Specifically, an allergic response may be triggered in people sensitive to the growth medium, usually corn, soy, or wheat. For example, residual wheat gluten has been detected on xanthan gum made using wheat. This may trigger a response in people highly sensitive to gluten. Some consider this to be a separate allergy to xanthan gum with similar symptoms to gluten allergy. Xanthan gum is a "highly efficient laxative", according to a study that fed 15g/day for 10 days to 18 normal volunteers. Some people react to much smaller amounts of xanthan gum, with symptoms of intestinal bloating and diarrhea.
when buying/using xanthan gum, do some research. find out where it comes from and what medium it was grown on.
if you are a celiac that is also super sensitive to corn or soy, i recommend using guar gum instead.
more info here