Severe heartburn symptons that nothing stops including surgery

I have had severe chronic heartburn for 4 years. Pain always on right side of chest, right side of throat and mouth, and right side of back especially just under shoulder blade. None of the medications prescription or OTC help. No diet modifications help. Pain is worse shortly after eating and much worse at night. I sleep sitting up in a chair and still have pain that limits sleep. A month ago I had the surgery Nissen Fundoplication. That has not helped. I no longer think acid reflux is the problem but so far my Doctors are reluctant to look for anything else. Any idea what could be causing the pain.