I found my dog to have red bumps also that turned crusty, turns out it was a form of mange. I saw the mites myself under the microscope when the vet showed me. I found treatment at the feed/farm store. A spray called Vetericyn, worked soo good for my puppy. I tell everyone about it. It works on hot spots too. amazing stuff.
Editor Note
Thanks for your comment. Vetericyn promotes skin healing, it does not kill mange mites. A good idea is to use a dip such as Dermisil (lime sulfur) followed by use of a spray like this one to speed healing.