Undiagnosed Abdominal Pain going on month 4 in teen (15)

My son started having pain end of January. Beginning of February he told us one morning when he had severe pain and we went to the ER thinking he has appendicitis. At the ER he was diagnosed (CT scan and XRay) with pneumonia (yes we were surprised). The pain was attributed to the pneumonia and possibly inflamed lymph nodes. After 4 rounds of antibiotic his pneumonia was cured but he still had pain. He has been making his way through numerous tests: multiple Xrays, ultrasound, blood tests (even with pneumonia his blood test was normal), endoscopy, colonoscopy with biopsy, upper GI with barium, a CT scan when it forst started and another recently (second one with oral contrast and IV contrast) and all these tests say he is perfectly healthy. He has baseline "level 5" dull abdominal pain and intermittent sharp "level 7-8" flare up pain. The flare ups happen the more he moves though as it is getting worse (more and longer flare ups) he has them as he wakes up. He has been taling amitriptyline to see if it abdominal migraines for 6 plus weeks to no avail. That does help him sleep which is good as he was starting to wake up from pain. Notable is that when he was coming out of the anesthesia from the colonoscopy he was in agonizing pain (writhing in the bed, clutching the rails and my arm, tears rolling down his face) that took two doses of fentanyl to manage (not go away). He was at an elevated pain level after that for multiple days. The only test still on the schedule is exploratory surgery. Myson is at his whit's end. He was always active - wrestler, lacrosse player. He missed his wrestling regionals and beyond because of this pain. He needs relief! Help please.