In my experience shaking or shivering almost always means pain (unless it's 5 below zero). I'd get him to the vet pronto - and I'd pick a new one if your dog has a smelly wound and your vet is not concerned. Also - fat deposits don't usually rupture. What you're describing is probably a sebaceous cyst. They can heal up fine, but need proper wound care. Let us know how he is, poor boy...