Why won't my dog stop licking?

Licking, chewing, scratching, and self-biting are common symptoms in pets. Dogs will scratch repetitively with their paws or gnaw incessantly; target areas can include the whole body, or specific areas, like the backside, legs, and feet. Regardless of the form of the symptoms, when they appear in excess, they point to one thing: itchiness. Known as pruritus in medical terms, itchiness is among the top reasons owners take their pets to veterinarians. To fix the problem, a vet must find the root of the problem

I agree that the previous answer is most likely the reason. There is a lesser possibility that it's triggered by boredom, often a result of insufficient exercise.