Hot spots are not uncommon, and while uncomfortable for the dog, they shouldn't be all that serious. Definitely take him to the vet, they may want to shave the area around the spot to expose it to the air, and if any of them are infected you'll need antibiotics. When Halo had one (HUGE!) they also gave me a drying powder to put on it. The most important thing you can do right now is prevent him from licking the spots. If you don't have a cone for him to wear, you should buy one right away. I got Halo this collar, which worked very well, but I had to get it online and wait a few days for it to arrive: Home Page
It prevented her from turning her head far enough to lick the spot, but she could still eat, sleep, play, and use the dog door wearing it. I'll find some pictures to post later.