Allergies to gluten is typically diagnosed for kids, not for older people. A gluten allergy is genetically determined and manifests during the first years of life. Kids with gluten allergies (caliacia) experience diarrhea, bloated abdomen and grow slowly. Slow growth is due to the malnutrition where many nutrients are not absorbed by the intestines but expelled through the stool.
In your case, malnutrition and other symptoms seem to be due to the gastric bypass surgery not to a food allergy. In fact, malnutrition is the main goal of the surgery, to reduce the number of absorbed calories. But the problem is that beside caloric nutrients there are also some very important non-caloric nutrients (vitamins and minerals) that are less absorbed, too. A deficiency of those non-caloric nutrients can cause serious health disorders. To prevent a deficiency, you might have to supplement your diet with non-caloric nutrients.