It can be difficult to identify the cause of lesions - ringworm is easily diagnosed by a culture, as is flea allergy, but there are other possibilities. Have you seen him scratching? You need first to check if he is doing it because he is itchy or sore, or if it is the result of a fight. If he is doing it, then is it at the site of an ijury that is healing, in which case toy may need to put an ecollar on him to stop him for a few days. If it is something else, then it could be an allergy, or some other form of eczema. My Bonaparte had his neck and chest covered with red raw patches that he was scratching and the vet could not decide what he had after ruling out ringworm and external parasites. He gave me various creams to apply and anti-fungicide tablets. But those didn't work, and I took his collar off to relieve any irritation that it was causing. The problem cleared almost at once, and now, by trial and error, I have found he has a metal allergy. With an all-plastic collar he is fine. SO keep experimenting and observe his behaviour closely.