Hi Jacqui welcome! Here are some ideas to stimulate kitty's appetite http://www.felinediabetes.com/FDMB/threads/suggestions-on-how-to-stimulate-kittys-appetite.130770/
Are you testing for ketones? This is very important especially if he's not eating well. Can you please give us some more info? Are you home testing, what and how much insulin, what are you feeding, are there any other health problems?