Poor Clayton. Did the vet say what the back leg paralysis is from? What 3 meds did he give him? What is he treating him for besides the URI? Did he mention that you need to give probiotics while he is on the antibiotics? That is EXTREMELY important because the antibiotics kill off the good gut flora so his appetite will decrease even more. What dry food are you giving him? Before you actually start forcefeeding, it's important that you put a little on his nose to see if he will lick it off first each time so that it causes as little stress as possible, he is going through enough right now. Meds are also very drying so you need to make sure that he gets frequent baths and oral fluids.
Skittle is cute, any idea how old he/she is? How long is it from nose to tip of tail?