Firstly, I want to ask you that when the dog came to your place, have you asked his previous owner what food he fed him? Its my exp. with my lab, when i adopted him at the age of 2.5 yrs, when a dog changes his place, generally he would take 1-2 months to adjust with new food if not provided his food habits. Even my lab had many times stomach disturbances in that period. But gradually, I care for him for his food and he adjusted fine. I avoid pedigree and now giving him home made food, chicken or meat twice a week, curd in each meal. The question of Dermatitis was also with my dog when he was abandoned, but as you are going with treatment, it will be ok with the time and be careful for this season, do brushing daily. Remember the quote-- Love can cure anyone. So happy petting..