This can be serious if it stays out of its sheath for any length of time. Sometimes it will only happen once and then never again- which is why your vet was not concerned. Now that it has happened again it needs to be re-addressed with the vet. If he is still unconcerned then find another vet for a second opinion. They may need to put him on something to relax him. He also needs his prostrate checked if they did not do that then. Fever is not normally caused by this so I am not sure what is going on with that.
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