You are the only person I have ever seen with a father with dermatomyocitis. My father has it as well. He was diagnosed at age 18, well before I was born but has struggled his whole life.
For the original poster, a few thoughts come to mind:
Lyme Disease or other tick-borne diseases (explain the temp and pain)
Autonomic Dysfuction (would explain the temperature)
Kidney Stones (extreme pain but I would have thought they would have looked for these)
Nerve pain stemming from spinal issues
Fibromyalgia - yes, the pain can be that bad
Since the painkillers aren't helping much, it makes me think that it might be nerve related. I hope that your dad get a diagnosis soon.