Pain in the Butt!

My Piriformis Muscle has agitated the Sciatic Nerve and I have already posted about that. My problem now is a really deep pain in the bum and it does not improve with painkillers I have been prescribed by my GP - Co-codamol. The GP then prescribed Naproxen which caused tremendous swelling of my ankles and legs so I had to stop the drug. Can anyone suggest an alternative pain killer for the problem please? I am waiting to see a Doctor in the Pain Clinic. The problems started just over 1 year following my THR