It sounds like your dog has a hot spot from the licking. These happen frequently in the warmer weather. The dog continuously licks or chews one spot on the body until it develops an open sore, and the sore grows from the licking or chewing. It may also become infected. If that is the case antibiotics will be necessary.
The spot will need to be kept dry which means you'll have to keep the dog from licking it. You may want to invest in an Elizabethan collar from the vet, keep it handy because these spots show up frequently through the summer months.
If the area is not infected shave the area around the wound down, wash frequently through the day with anti bacterial soap and dry well. There is a product called nf puffer put out by Hess& Clark that can be found in a farm feed store (possibly in the horse section), get that and apply through out the day.This will help with infection and will dry the spot up. IF you chose to go to the vet and get antibiotics then you should see a difference in about three days.
Here is more on Moist Dermatitis: (hot spots)