We have things in common Karlin. We have had the same addictions...pain killers/heroin. I started the same way...but I had dabbled in drug use before...no addictions, but just recreational use. Then after I broke my back as a gymnast, I became addicted to pain meds; and it went from there.
At any rate; now that I am clean, I don't feel the same pain. In retrospect, I think that my mind intensified the pain because my mind knew that if my body felt pain then I would be "rewarded" with drugs. I think I had a lot of pain that was not as severe as I had thought. My mind had a way of dwelling on little amounts of pain, and fooling myself into thinking it was not bearable; and then I would use out of "need". Now that I KNOW that I will NOT be using drugs; my body has learned to not focus on the pain...now if something hurts, I know I can overcome it.
Have you tried a methadone clinic? It sounds to me that methadone would be a wonderul treatment for you!