What insulin, dose, and how long since insulin?
Any vomiting?
When you offer food, does he lick his lips and turn away? That would suggest nausea.
Is he crouched down and hanging his head like he doesn't feel well? We call it "meatloafing".
My signature link Secondary Monitoring Tools has 2 methods for checking for dehydration - the neck scruff and the gum test. If you pull up the scruff and let go, does it snap right back or does it stay pulled up (tented). If tented, then he is moderately to severely dehydrated and you might want to get to the vet asap.
Smell his breath - does it smell sweet or like nail polish remover? If yes, that may mean ketones are present. In that case, I would take him to an emergency vet.
