15 y/o in daily pain - not IBS

My son has extreme, lower abdominal (below belly button) sharp and constant pain every morning. It wakes him up about 6am and does not go away for 4-6 hours. Some days he is constipated, others diarrhea. BM sometimes brings relief, other times makes the pain worse. Have seen 5 gastro drs and other pcp but no one knows what it is or why it has continued for nearly two years. All drs did agree it is NOT IBS. Has had endoscopy and colonoscopy (where 1st gastro diagnosed as mastocytic colon due to increased number of mast cells in the colon). My research brings me more specifically to mastocytic enterocolitis. However, after all this time and the dozen meds we have tried, he still has no relief. To name a few, Bentyl, cromolyn sodium, periactin, Pepcid, Levisin drops, methocarbamol, OTC ibuprofen/Tylenol/aspirin. We've also tried aloe vera juice, peppermint oil capsules, probiotics; fiber and Miralax. Three days ago he started 2 doses/day of Braggs apple cider vinegar. He is currently on cetirizine, Pepcid, and just started amitriptyline 25mg at night to see if that will control the cramping. Bloodwork and allergy testing completely normal, tested negative for Chrohn's. Considering stress management/MH therapy as it is affecting his mood daily. Due to excessive absences, he almost failed 9th grade and so far has not gone to school at all (10th grade started last week). Anyone have any suggestions? I am beyond frustrated that I cannot help my only child. Thank you in advance!