I would talk with the Vet
From what I understand, diabetes in cats is not always easy to deal with and may take test after test to determine the amount of medication it will need each day.
I would either go back to the Vet or find a different Vet.
I did not elect to treat my 18 year old cat with diabetes, years ago, and had him put out of his misery. He was too old and too cranky to go through all of the testing and treatment.
From what I have learned, diabetes is often created when the cat is over weight. That is not always true, but in my cat's case, it was true...so I now make every attempt to keep my cats on the slim side. Of course, diabetes is not the only threat to their lives. I have proof of that, having lost two cats for other reason(s) just last month.
Good luck and keep us posted. I am sure other folks will have some good advice for you!
Sas