Severe upper abdominal pain in 12 year old

My son has had severe pain, very localized on his upper right abdomen up under his rib cage for the past 6 months. It came on very suddenly and has been constant and severe (8-9/10). He had many tests done with no answers before being referred to a pain clinic where he has been a patient the past 3 months. He has been given a vague diagnosis of a nerve injury or myofascial pain. He had a nerve block injection in July which was not successful, however the lidocaine injection that preceded it did relieve his pain for about 30 minutes. He has a rigorous physio therapy and psychology regime, and though his coping and function have improved he has had no relief of pain. He is vomiting daily from pain and only managing 1-2 hours of school daily (with a huge effort). He has been able to be very active, but needs to regulate the intensity of activity as deep breathing increases his pain. There seems to be some connection with the diaphragm/psoas. Just looking for others who have perhaps dealt with similar issues and ideas of what has helped. So far nothing provides even the slightest relief.