Epigastric pain. Specialist to consult.

My friend is suffering from epigastric pain from last 13 yrs and he has undergone all the test in this 13 yrs be it endoscopy,ecg,echo,tmt,ct scan thoracic blood test all the reports was normal,he was prescribed acid blocking medications like rabeprazole,pantaprazole,esomeprazole but nothing helped as his condition was not getting better the doctor told him to consult a pschytiarist the doctor prescribed him fluoxetine 20 mg,paroxetine 10 mg,olanzapine 2.5,lithium carbonate 400 mg,he was on this medicine for 1 yrs ,it helped him but as soon as the medicine is tapered all the symptoms come back and due to the side effect of this medicine he got neuropathy in the upper back,I want to know from what disease he is suffering ,right now he is on medicine like pantaprazole and pregabalin for 2 months but his epigastric pain and upper back pain is not improving,I want to know which specialist to consult.