I've been taking Methadone for 17 years. I'm now allergic. Is there a substitute?

I use it only occasionally for pain. I have SLE w/Peripheral Neuropathy. I never became addicted to methadone, fortunately. Methadone is perfect for the outbursts of pain I have now. In the beginning, I had continual nerve pain. Mostly in my feet. I take several drugs that also help my SLE & nerve pain. (Such as: Effexor, Amytriptyline, Imuran, Neurontin, relafen, Plaquenil (For my AFib I take Eloquis, Tenormin, Statin). I don't know why, after 17yrs I've become allergic. I would like to find a substitute for my outbursts of very painful neuropathy. When I was first diagnosed w/SLE. My neuropathy was in my feet, legs and my hands. I could not walk w/o a cane. It was so unbearably painful. I took methadone 10mg every 6hrs. Although 17yrs later, only my feet hurt all the time, but it is the occasionally that the nerve pain reaches a pain level of 12. I need to find a substitute now because of the itchy rash I got from methadone. Any suggestions?