Because of your condition causing nerve pain, the best type of medications for that are not opiates, but medications like Lyrica, Neurontin (gabapentin) , Topamax, Celebrex, Cymbalta and the old tricyclic anti depressants work wonders for neuropathic pain.
The fentanyl won't do much for nerve pain, that is for mechanical pain but I would definately talk to your doctor about trying one or more of the medications mentioned above since they work well in treating pain caused by nerve damage. You do have to be a bit patient though because those type of meds can take a few weeks or even months to find the correct dosage for you to get good results from. The side effects usually go away after a few days to a few weeks once your body acclimates to the medication.