one of my maltese have serious allergy, small black sores just look like bites , so i brought her to the vet, the vet said that my dog is too allergic... he gave me some antibotics and taught me to bath my dog with a shampoo, named malayseb (bath 3 times a week ) no snacks, eat nothing except eukanuba~ for skin and coat, response FP..after 2weeks treatment, she is getting better now.....when i asked my vet how comes that my dog have this allergy...he said maybe the grooming place (petSHOP) is not clean and contaminated with virus or bacteria,,,, maybe when i brought her out, she was infected by other dogs,,, so the allergy becomes worse... small black sores appeared !!! maybe you can asked your vet if your dog need to change other dog food which is good for skin, wash your dog with medicated shampoo...
hope your dog will get well soon