My son has been for after feeling ill for over 2 months. he eats and then almost immediately has to use the bathroom. the scope showed no ulcers etc and was clear. he has lost over 10kg on the last 3 months and when eating certain foods feels ill?

Colonoscopy: Did the endoscopy include both the upper and lower GI tracts? If not, this is recommended. Food allergies and intolerance is another cause, but the weight loss also increases the likelihood of infection. He should have a chest x ray, COVID 19 screening test and food allergy panel, IgE and CBC, diff and platelets as part of his workup. In the meantime, provide fluids, protein sources, a probiotic.