My 14 year old kitty Shadow was crying all the time over the past 2 weeks (last week and the week b4 that) and we took him to the vet and after blood tests and urine tests were informed he was diabetic. I found this forum by searching online about the disease and am always on it too now. I have since changed him after the results from the vet (immediately last Wednesday eve when I found out online here what is suggested to do) to only canned high protein, low carb (mostly Wellness Grain Free) and he doesn't cry like he had been at all. I am now doing 4teaspoons of one kind of wellness (ckn and herring) and 1 tsp of just chicken wellness (about 1oz) 6-7 times a day throughout the day with water added to the canned food and he's doing great. We are very lucky and it looks like the change in diet may keep him off of insulin. I started tested his blood glucose levels after learning what to do here and his bg is still higher than we'd like in the a.m. (today it was 132) but during the day it ranges from 66-77 so we're excited. His blood glucose results from the vet's were 366. I read how much that increases due to kitty's stress going and being at the vet as well as from the high carb dry food he was always eating.
If I were you I would go out and get some high protein, low carb canned cat food and start him on that asap (maybe small cans til you know what he likes and not to upset his tummy). There are links on this site for help with transitioning to all canned, luckily Shadow loved it already and only eats one to two pieces of our lab's grain-free evo kibble at night when he's not looking as far as any dry food is concerned.
L