Honestly it depends on what it is. If you get one antibiotic and its not made for that type of skin condition it can get worse! Trust me I work at a small animal vet. To ease any of it get an oatmeal based shampoo to hold you over until you can get him to the vet and get him a medicated shampoo.
What kind of a skin problem? More information is needed - better yet, take him to the vet and find out what is behind it - that way you will know how to treat it effectively.