Bald spot near the tail. The dog has been aggresively biting the area/ I have been spraying hot spot medicine in the area for awhile. I noticed from an angle in the sun under the hair it looks really red and irritated. I gave her a bath with flea and tick shampoo and gave her flea and tick medicine. I don't see any evidence of fleas. What else can I do and I wonder what is causing it?