Pheochromocytoma-like symptoms with no sign of a tumour?

My 16 year old son has been suffering from debilitating symptoms for the past 5 years. It began with a very sudden onset of excruciating pain in his right upper quadrant (under rib cage), accompanied by headaches, nausea, sweating, extreme anxiety and panic attacks, terribly disrupted sleep, extreme fatigue, tachycardia, heart palpitations and chest pain, musculoskeletal pain, and weight loss. Imaging Investigations have been normal (brain, spine, abdomen MRIs), and he has undergone significant psychiatric therapy, and more than a dozen medications which have only made symptoms worse. He recently did 24hr catecholamines/metanephrines tests- the first came back 3-4x normal levels for epinephrine, norepinephrine, metanephrine, nor metanephrine. But subsequent tests were normal. It is looking unlikely to be a pheo/para. But I’m wondering what else could cause these symptoms. The endocrinologist felt the symptoms were catecholamine-involved, but wasn’t sure what that would be if not a tumour. My son’s quality of life is so poor and seems to be increasingly worse. He is unable to go to school or participate in almost any activity. Just getting to doctors appointments is a huge task and wipes him out for days. I am desperate for answers, or a direction. Our doctors seem to be stumped and have become a bit apathetic because they don’t know what to do. Willing to go anywhere to do anything- just not even sure where to look. Thank you.