We can help, but we'll need a bit more information to do so.
It sounds like you are home testing his blood sugars? If so, what type of meter? Would it be possible to put those blood sugar values you've been getting into our version of a spreadsheet?
What type of insulin is she getting? Being at 3 units so soon after starting insulin is a higher dose than we'd start with. One possibility is the dose is too high and the cats body is reacting by dumping sugars into it's system.
Also, what food are you feeding him? A lot carb wet or raw food diet is best. Cats on a higher carb dry food diet will need more insulin.
I have lots of questions, as will others have before we can suggest why the high numbers. Which is not uncommon for a newly diagnosed cat. If you could put the answers to my questions in your signature, that'll be a great start. More in information on what we are looking for in this post.
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