I know all this because the exact same thing happened to my son. Nothing would take his pain away,
in spite of being on high doses
of methadone, which eventually stopped working. Amazingly enough, once he withdrew the methadone, the pain subsided. It got worse during the withdrawal, as expected, but once his body was cleared of the addiction, the pain was so minimal it was manageable with OTC stuff and eventually he didn't notice any pain.