I don't know if I will be much help with your problem. There are two issues you are struggling with; one being tolerance, where any pain medication will slowly lose effectiveness, and the other being the anatomical source of the pain. Any relief from a narcotic (oxycodone, hydrocodone, demerol etc) will, be shot-lived; The receptors for pain medication in your brain simply adjust to whatever you are taking, and the dose must be increased to relieve the pain again. At some point you will run out of room to keep going up on the dose.
I don't know what the source of the pain is; if you have scarring in the muscle you might be able to find exercises through physical therapy that will help keep the jaw muscles relaxed and less painful. Muscle relaxants like flexeril or skelaxin are sometimes helpful. If the pain is from nerves, medications like Lyrica or gabapentin sometimes help. If there is a component of depression, Cymbalta might by helpful. All of these non-narcotic medications are better choices than narcotics, as they are not subject to the tolerance that is such a problem with the narcotic medications.
I had tmj surgery and ended up on many pain meds. What to do ? I can get off the meds the pain is at the door waiting on me....
Seeing an orofacial pain specialist is advised.