You need to take it to the vet, if he has been licking or scratching at it a while, he may have caused a secondary infection that will NOT heal on it's own. He will need an antibiotic from the vet to help with it & maybe a cortisone product to help with itching & inflammation. The vet will be able to tell you "what" the sore is or is from as well. The vet may seem a little pricey but, your dog will thank you for it in the end...
