Not much I can suggest without pictures. Might be a infection, might be a feeding wound, might just be him rubbing on something. If you use neosporin or any other antibiotic ointment make sure its the regular stuff with no "pain relief" stuff in it. Also you are better off getting the AAA or whatever the cheapest antibiotic-no-pain-relief-ointment you can get as the name brand stuff is no better than the cheap stuff.