My mouse has scratched his neck and side bloody and removed his right ear...?

You could always bring him back to the vet and have him checked for ringworm (fungus), Mites, lice(also called louse) and any other parasite because it definately sounds like that. Ask your vet to prescribe Revolution and and anti fungus cream. Treat until there has been no symptoms for at least 1-2 weeks or more because they can become resistant to the meds. Definately talk about getting a stronger antibiotic and maybe doing some soothing baths. Definately sounds like internal mites though they cannot be seen by the naked eye. Good luck to you. If he is suffering too much it might be his time. You will know when he wants you to give up.