Gall Bladder

My 11 year old son has been dealing with illness for 5 weeks now including extreme fatigue (up to 22.5 hour out of 24), no appetite, pain in forehead and back of neck, joint pain, and abdominal pain. He has had five rounds of bloodwork from general CBC, liver function, mono and CMV virus screening, lyme testing, lypase/amylase, thyroid testing...and was admitted to the hospital for further evaluations with a guarantee of an answer from his doctor. We were there for 3 days and during that time he had an mri of the brain and ultrasound of his abdomen. MRI was normal but ultrasound showed that his gall bladder was very small. This aligned with his bilirubin counts being elevated for the weeks leading up to the hospitalization. Doctors said they believe head is migraines and he was put on the common magnesium and riboflavin supplementation. They tried to convince me that the gall bladder is Gilbert's Syndrome and said it is a genetic condition from the mother's side. Thing is there is no history of that. Also they implied that he had jaundice as a baby and at times throughout his life this far which is absolutely not the case. He is diagnosed on the spectrum, has adhd, sensory integration disorder as well as anxiety. He has lost 10 lbs over the last month and after the weight loss he was at 100 lbs spread over his almost 5'6" height now. He is so incredibly thin everywhere and his bones ( elbows, shoulders, spine, etc) are grossly showing at this point. He basically is refusing to eat saying he is not hungry. He will drink meal replacement shakes but that is not enough to keep weight on his ever growing frame. He is supposed to be scheduled for a HIDA scan sometime over the next month but am very concerned about the already deterioration over the last month. The follow-up with the GI doc is not until May 12th. When he eats greasy food the whites of his eyes yellow. Please offer up any insight or recommendations you may have. Thank you in advance!