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Hello and thank you for using this site to help you. If this is a spot he is chewing he has likely caused a hot spot and it sounds like it may be infected. When a dog chews an area the bacteria in the mouth causes an infection. Hot spots are moist dermatitis , meaning the skin is always kept wet usually through chewing.
The best bet until you can get to your Vet for antibiotic spray is to shave any hair away from the area, wash frequently through the day with an antibacterial wash , dry well and then apply a triple antibiotic ointment that does not contain Zinc oxide. Get a Comfy cone collar from your pet store or online and use that so the dog cannot lick it anymore,. See your vet for appropriate medication to help heal the wound. It may go deep under the skin.
I'll send you a link going over hot spots http://www.petplace.com/article/dogs/diseases-conditions-of-dogs/skin/acute-moist-dermatitis-hot-spots-in-dogs