Shingles is incredibly painful, so I really don't think that's what you have if you don't have any pain. Impetigo is a possibility, although it's most common in children.
Are the sores oozing anything at all or do they seem to rupture? The Murpirocin is an antibiotic ointment, so it should address the issue if it's impetigo- how long have you been on it? Have you called the doctor back to let them know that the itching has persisted? It doesn't sound like they gave you anything to address the itching- since the rash seems to be going away, I'd bet that it's addressing the infection as it should, but the itching will be uncomfortable for a bit. You can call the doctor and ask if there is anything you can take for the itch specifically.