thanks for posting on HCM,
Well his syndrome look more like a neoplasic syndrome i.e cancer-related signs i.e weight loss
, alternating fever
, stomach pain, history of GERD and surgery; his age. The combination of the above directs us towards presence of probable stomach tumor. Non-the-less they are other possible causes that could cause the pain + weight such as gallbladder
diseases etc. Your gastroenterologist is the specialist of choice for now to be seeing, just he will probably need to start looking further by doing other tests such as TNF, ESR, CRP, CT scan
, MRI etc to exclude other probable causes of your son's illness.
Hope this helps and wish you the best