Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'd like to help out you and Ohli. I'm sorry it has taken so long for you to receive an answer. I just came online and found you.
It's midnight for you, and you are probably asleep. It does sound like Ohli is stable medically, meaning he should be fine overnight. I'd recommend that he see your vet tomorrow however, if he still doesn't want to eat and is acting in pain. It's dangerous with cats to wait more than a day to see how they do. Cats that don't eat for a couple of days or more can get a serious secondary liver disease called hepatic lipidosis.
Hopefully, when you wake up in the morning, Ohli will be back to feeling fine. Please let me know if I can address anything more specifically, or if you have any concerns or questions.
So glad to be of service! Also, happy that Ohli is getting the care he needs. . .these FUO's (Fever of Unknown Origin. . .yes we have a name for them!) are really quite common in cats and respond well to antibiotics and good nursing care usually.
Hope he improves quickly!