I have a sick kitty. He has been seen by the vet and was diagnosed with a fever of unknown origin. The vet took X-rays and said he is healthy and he's not concerned. He gave my cat an antibiotic injection and an anti inflammatory. When my cat came home yesterday he was acting much more normal, eating and drinking and purring. Last night he became lethargic and hot again. Today he has been sleeping most of the day but did manage to get around and eat a bit. Now he is resting, but keeps shifting positions. He's streatched out and showing his tummy, but shifts around a lot. He is not huddled up or hiding. Could this be from the fever? How long does it take for antibiotics to start working and does his behavior sound like he's painful? He's 7 years old and has never been ill. He's an indoor kitty, but his brothers go outside. Thanks!