Helet! My vet hasn't a clue!
This rash is around my dog's mouth, etc, between toes, and it is dark pink/red with occasional sores. tried mange spray, no help. tried allergy medicine...nada. any suggestions? my baby is.miserable. I tried attaching a pic buto it's too large 
Skin problems can be very frustrating to deal with. Has your vet done already a skin scrape to get a better idea of what may be going on? Thinking here that the areas affected are place that tend to be moist. Yeast infections (malassezia) have a strong preference to lurk in areas where the skin is damp and doesn't air much. The mouth is obviously prone to staying humid when your dog eats, drinks or drools, the interdigital area (between the toes) also shares the fact that it's not aired much and dogs sweat through their feet (even though minimally) when they are stressed. These types of infections tend to be treated with topical anti-fungal wipes or pills. Of course, this is not a diagnosis, it's only a possibility,only your vet can give you a diagnosis through more testing and then if it turns to be fungal/yeast infections it can be treated accordingly.