What are sores that crystalize?

My son has sores that are popping up around his eye and on the inside of his thigh. He also has sores on the inside of his nose that are crystalizing and scabbing over. His nose is congested. He is autistic and prone to multiple disorders, but the doctor keeps putting him back on prednisone and cephalaxin over and over since these have developed and cleared up several times since April. Any ideas?