Fever of unknown origins

My cat buddy who is a 2 1/2 year old male developed a uti last week. We went to the vet and got it treated as soon as we realized what the issue was. 3 days later he started sneezing non stop. That progressed into mouth breathing, stuffy nose and watery eyes. We brought him back to the very today and he ended up having a fever of 106. She said she couldn't figure out what it was. He tested negative for feline leukemia. He had high white blood cells, high protein and low electrolytes from what i remember her saying. She said they were gonna keep him over night to get him fluids and his fever went down to 105 last I heard from her. I also found out that there is no one monitoring him over night and that worry's me sick but they're closed and there's nothing I can do until the morning. Any advice or encouraging story's are welcomed. I'm worried sick about this and have been for the last 2 weeks that he's been ill back to back. Please everyone take the time to pray for my baby😞