My now 18 week girl pitbull is more and more biting at her tail close to her but and the skin around her anus but not on. When I see her doing it I stop her she bites on herself all over the place all the time I took it as for sensitive skin. The only thing New to her diet is the banana yogurt blue buffalo treats. Everything the same. These bumps aren't in the areas on her tail but a slight pink in the area on her bottom by her anus. She doesn't scoot her butt across the floor. Her poop is a little softer at times no worms. Has been designed. Last set of shot this coming Wednesday. Please help I'm worried she might be allergic to something.