It is possible that it is diabetes. Do you know anyone that has diabetes and would be willing to test his blood? It isn't difficult...especially if the cat can be easily handled. We used a paw pad..you have to experiment by making the tester needle as short as possible and increasing length till you get a drop of blood. You really don't need much.

You could take him to the vet to test but you can also do it at home to save money.

Denyce