Humulin N + Zero carb dry/low carb wet food

My Ziggy was diagnosed as diabetic around the middle of July. He started on 2 units Humulin and gradually went up to 5 units. He consistently, in the beginning, tested over 599 or in the 500's. Ziggy is about 11 yrs old. Always drank alot of water but didn't show signs of stress until this early spring, post urethrostomy surgery due to blockage.

Since then he had a "perfect" curve done at the vet's. I saw the numbers. After that he was up and down...sometimes due to my not getting the shots right with a short needle (we've changed to longer) and I'm sure also due to stress of going to the vet.

I've since learned to home test. I've also embraced the dietary issues which I always did think was behind the diabetes.

He's been eating Young Again Zero Carb dry food since this past Saturday. Today is Tuesday. He also gets Fancy Feast pates and I tried integrating the Friskies he used to eat (on the low carb list) but now it seems to give him diarrhea. All he gets for treats are freeze dried chicken or turkey and YA sent me sample treats which he seems to like.

Anyway...his numbers haven't dropped as dramatically as I was lead to believe they would. He's been in the low 400's, mid-300's, since. Tonight he tested at 363. Today he got 4 Units Humulin N both shots.

My vet had him on 5 units, but that was before the food change. I've been following the facebook support page and testing preshot. The few times he tested low (below 150) I didn't give him insulin but I think that was only a couple of mornings.

I just don't know what to think or what to expect. How can I decide how much insulin he gets? Should he stay at a specific unit/shot each day regardless? I hate taking him to the vet because of the stress and I know that changes his numbers. I'd like to let my vet know how "well" we've been doing on the zero carb dry and Fancy Feast, but right now I'm not feeling so positive.

Any help would be greatly appreciated. Ziggy's acting fine...his coat is back to normal as is his behavior.