Welcome to the board!
The first thing that comes to mind is demodex mange, Kellynbobellen. One of our rescues arrived with it--she had some baldish patches but they didn't look red or inflamed, either. Demodex mange is more a disorder of the immune system than anything else--the vast majority of dogs have the mites that cause it, but only when the immune system is unable to keep them in check do you see mange. It most often occurs in young dogs whose immune system is still developing, and in dogs with compromised immune systems (in our Macie's case, her immune system was likely out of whack due to the negative effects of the stress of being rescued, rehabbed and adopted out).
If I were you, I'd make an appointment with another vet if you can't see your own, and ask for a scraping to be done. The reason I wouldn't wait is because if it's demodex mange, you may need to put off the surgical removal of the bump to minimize Charlie's stress, and you'll want to start treating the mange as soon as you can, as well.
There are other reasons for hair loss, as well, so the vet may want to do a blood panel as well to rule some of them out.