This sounds like when my Scotty has an abscessed tooth. He was given bloodwork, antibiotics, pain medication, anti-swelling medication and in a few days when his infection under better control take to surgery, the tooth removed and an I&D done. He also had developed a gunky eye and the infection spread to near to his ear canal. It was a vicious bug that the vet cultured that first day so he would know what best to give him and indeed he did change his antibiotics to a quite costly one per the culture results. He went to the vet daily for a while as the thing flared up so suddenly and was so very aggressive. I believe he kept him overnight that first night and had his vet tech stay with him just in case.
Hope that your vet can get to the bottom of this fast. Some of those bugs are very bad and hit very hard. Vet was worried Scotty's would get to his brain. Thankfully I got him to the vet ASAP and he hadn't even lost any weight as he'd been eating normally until that day I saw the blood on his muzzle and gunk in his eye!
Can't imagine the pain he must have been in, though he had no running pus yet but the swelling was awful. Overnight his eye and muzzle/nose had become distorted due to swelling. It was a close call but vet acted fast and aggressively to fight the bug.