Wow. Okay, if he had a BG of 205 13 hours after a dose of 2u of Humulin, that's actually really good news.
Like BJ said, Humulin usually will only last up to 8 hours.
However, that also means that most likely that 2u dose is too high. One of the reasons he may feel lousy and just laying around is because he doesn't need as much insulin as he is getting.
I noticed his one paw was swollen
Front paw or back paw? Is it still swollen? Does it feel hot? If you squeeze it, does he react like it hurts? He may have something wrong with his foot or, like he sprained it, or he's got an infection of some sort.
Do you know how to tell if he is dehydrated? Pinch up a hunk of fur and skin on his back and see how fast it returns to place?
The sequence of events just sounds "off" to me. You said you brought him in because he wasn't eating at first, then found out he was diabetic? Usually a diabetic cat will act like he's starving and eat like a pig, but will continue to lose weight. Do you know if there was anything other than elevated blood sugar in the cbc results that would indicate any additional problems?
If you want to try to manage this at home, here are the first steps you should take...
1 - go buy a human glucometer and test strips at a pharmacy or walmart. You can test his BG at home by yourselves and you'll be able to tell at any given moment where his blood glucose level is at. You need to know it is high enough when you give him a shot so that it is safe to do so. 2u of Humulin can have a very quick and harsh effect on his BG, and if it isn't high enough, you can cause his BG to drop to unsafe or deadly levels.
2 - call the vet and ask for specifics on the cbc numbers. What was "outside of normal" levels on the test. What was his BG on the test? If you can get that info, we can help you understand what all the numbers mean. Also ask the vet if he would consider prescribing another insulin, one that is appropriate for a cat (because Humulin is NOT) like Lantus, Levemir or Prozinc. They all last longer and are more gentle.
3 - reduce the amount of insulin you are giving him to 1u until you can get a meter and test him.
4 - feed him anything he will eat for now. If he goes a day or two without eating, it will cause all sorts of additional problems that could put him at risk.
There are hundreds of people here who will do whatever we can to help you and your kitty. There are thousands of cats still alive after being diagnosed with diabetes that are living proof of that. If you want our help, it's there and it's free for the asking.
Carl