Get rid of the fleas. Some dogs are very sensitive to flea bites and will bite, scratch, and dig holes in their skin from just one flea bite. This can happen even if the dog has had fleas before and dig not dig dig dig. My dog is going through this right now. He has had fleas in the past and I did not even know it because he did not scratch at all. Last week he started digging and in two days had dug holes in his self. I broke down and used Revolution on him. Yes it is bad, but it works and I had to do some thing for the poor dog. I have been putting Colloidal Silver on the places where he dug holes in his skin and it is helping. I only found ONE flea on the dog.
Good luck. Over the counter flea remedy will just aggravate the dog's skin more. I would suggest that you call your vet.