High Fever-Possibly Distemper?

I’ve had 7 cats before in my life, one of whom I raised as a kitten from four weeks old. Now we have two new kittens we rescued two weeks ago from a stray/feral cat outdoors who was killed by a raccoon when they were about 3-4 weeks old as well (so they’re 6-7 weeks old now). Yesterday in the early evening, one of our kittens got really lethargic and wouldn’t play with his sister even though she was zooming around as usual and trying to climb all over him and stuff. He would just stay in the bed and look at us with those tired eyes you get when you’re sick. He’d still eat, but wasn’t interested in running around. This morning I noticed his breathing was rapid, so I decided to take him to the vet. His fever was 105, poor thing, and the vet said he had a sore throat. He has no coughing, sneezing, or runny nose, and neither has he been vomiting. The vet mentioned that he hoped it wasn’t feline distemper, since that kills most kittens rapidly. He gave our little one a shot of antibiotics and fever reducer (and who knows what else) and gave us meds of the same to give him every 12 hours. He said that if he refused to eat or drink, or looked even worse tomorrow, to bring him back in right away.

The vet recommended that we separate the two siblings to keep an eye on whether he’s eating, drinking, vomiting, gets diarrhea, etc. I have him in a playpen, and now he’s running around and playing, chasing his tail, trying to get out repeatedly, etc., so I hope that means he’s not on death row (yet). He also did eat. With that being said, does anybody have experience with handling feline distemper in kittens? Or FIP? Or anything that can cause a fever and sore throat? The next step is blood tests, obviously, but I only had enough money in my pocket today for the exam and meds. Do these symptoms sound like distemper or anything else? I know I can’t get an official diagnosis here, but I know that since so many of you are experienced with kittens I’d like to see what your experiences have been.