Sounds to me like the bike is not the culprit. If I were having your problems , which I do sometimes , just different areas of my back , I would go to these people to try and get it fixed.
https://www.airrosti.com/ Myself , my wife , son , son in law have all went to the one in New Braunfels with great results . Plus , I don`t think anyone moves around on they're bike more than I do . LOL