At my wit's end - looking for help

My son is 18  - 5'4" and 250lbs - he was diagnosed with a hypoactive thyroid 4 years ago - at which time his short stature was questioned with no outcome other than his bone age was 20+. We have visited several clinics and done many tests - looking for pituitary and othe issues but have found none. The only diagnosis that sticks is the hypothyroidism - now on a T3/T4 regime. He has repeatedly tried to lose weight but only seems to gain it. His hair is thinning (on his head) but elsewhere is quite noticeable - Onset of puberty, was as I recall - normal. At 16 he had his gall bladder removed due to atrophy

I do not know what to try next - some help is appreciated