It would help if there were more details to this question! And since there isn't, I really can't help you. So, due to that, I would recommend taking him to the vet.
You should take your animal to a vet. Swelling isn't a good sign especially if you introduced something new to their diet or some kind of medication. Take that pup to a doctor
Have you introduced your dog to a new food, treat, or medication? Has he been around another animal that could have bitten him? Has he had any dental problems or a broken tooth? If any of these sound like possibilities, take a look at this website: Either way, you should take your dog to a vet, especially if he isn't eating or drinking, but reading the article might help you and your dog's doctor figure out what the problem is! I hope this helps!
I don't know, but it could be a bad allergic reaction. You should take your dog to the vet.