Diabetic Cat and Stress?

We have a 8 year old cat named Benny, whom we got from the humane society at around 6 months of age. Whenever we need to take him onto the vet, he needs to be sedated. He roars so loudly that he disturbs the other cats at the office. After his last visit around 2 weeks ago, his glucose number was really high..around 480. The vet put him on insulin, 2 shots per day, 1 unit in each shot.He was also changed over to HIlls Science M/D cat food She wanted us to take some reading in his home environment to see if his numbers would change. We were told to only take reading on the weekend. This past weekend, his Sat morning number was around 310. The reading went pretty OK, little struggling. However in the afternoon his number jumped to around 380, we had to try and get the sample like 6 times, he's fighting us whenever we try. This afternoon his number jumped again to around 395 from 371 this morning.

Can the stress from the shots cause his numbers to go up? We also have twin 3 year old who run around a little faster than he likes.

We're afraid if we can't get this under control, we'll have to put him down......any suggestions would be greatly appreciated.