Artificial Emotion, I'm really sorry that you're having to deal with the nerve pain. I also deal with nerve pain involving my Trigeminal Nerve, as a result of multiple surgeries. It's shitty, but I've found mine to be fairly manageable with drugs like Gabapentinoids.
The issue man, that you know as well as I do is that we can't diagnose you or tell you definitively what is going on. I feel like I can be of some fairly limited help in providing you with my anecdotal experience with Methadone injection. I too have made the EXTREMELY IRRESPONSIBLE decision to inject some of my take-home dosages. I never went intramuscular, but I did go intravenously maybe half a dozen times. Mind you, this is not the nice, clear Methadone solution that some get. Mine was the fairly viscous, sugary, cherry flavored liquid that just screams, "you are a fucking idiot for injecting me", but, alas, the urge can be pretty strong, as you and I have demonstrated.
I've always had fairly decent veins. I'm thin and my peripheral veins are easily visible and accessible. I've always tried to maintain proper technique; fresh equipment every time, rotating injection sites, sterile water, all that jazz. I had never blown a vein, I think because I as fairly diligent about rotating, but after injecting that solution into my Cubital Fossa a couple of times, the vein receded and I could no longer access it. The next day, I found that it was quite hardened.
Luckily, the vein came back to me. I didn't inject Methadone solution again and counted my blessings that nothing went terribly wrong. When we mistreat our bodies, it matters. Methadone itself is considered to be fairly caustic, but combined with all of the fillers and the sugar and everything else, it's gotta be just awful to inject anywhere in your body. I'm not sure if the injection is what is causing your pain, but at this point, I feel like it's more important to just treat the pain than to worry about what caused it. Again, I'm sorry that you have to go through this man.
