Given your son’s symptoms of vomiting immediately after eating all the medical investigations seem to be OK (upper GI endoscope, diffuse scalloping of duodenum biopsy showed mild pathology, possibly early Celiac Disease; Swallow test within normal range, Ultrasound gallbladder/liver only few floating cholesterol crystals, X-Ray of colon area showed no masses or strictures, excess fecal matter, STD testing) ...he could be experiencing bulimia. Bulimia is an eating disorder due to psycho-emotional disorder. During bulimia, a person experiences an excessive eating followed by vomiting. Body weight can be normal or decreased. Frequent vomiting can create acid reflux, chronic inflammation of the esophagus, inflammation of the mouth mucosa and gums (stomatitis and gingivitis) and tooth decay. The only medical test that remains is a colonoscopy. If the colonoscopy is ok, you can ask for expert help from a mental health doctor in the treatment of the condition.