It sounds as if he has a swollen lymph node. There can be a few different causes for this. The simplest cause can be an infected tooth, or a minor infection. Though an infected tooth would normally cause a dog to be wary of eating.
But there are also more serious causes. So the best thing would be to try and see a vet as soon as you can, for this swelling to be examined.
This would probably wait till early next week, (?) (I am not at all sure of that)...but the best solution would be to get him seen by a vet as soon as possible.