Aw, poor puppy!
Make sure they do a scraping on Monday to rule out demodectic mange. Our Macie arrived with a mild case of demodectic mange--it's not too unusual in pups or dogs that are stressed (Macie was 18 months old, but had been in a rescue so she'd experienced a lot of changes in a short period of time). Macie had reddened areas with hair loss. She never got large open sores, though. We caught Macie's mange in time that we could treat it topically--but sometimes demodectic mange needs stronger treatments like dips or ivermectin.
Of course it could be something entirely different. Good luck at the vet tomorrow! Keep us posted!
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."