Welcome to FDMB.
I'm not sure that I agree with Lori about whether this is hypoglycemia or not. It may be that Jake is not yet regulated.
This is a list of symptoms associated with hypoglycemia.
* glassy eyes - it may look like cat is staring into space
* abnormal hunger
* restlessness
* meowing, crying, yowling, or vocalizing in a way that is unusual for your cat
* sniffing around (like a dog)
* dilated pupils
* laying, sleeping, hiding or curled up in an unusual location of the house
* vomiting
* cat looks/acts 'freaked out'
* problems with eyesight
* unusually aggressive (hissing , swatting, etc.)
* unusually overly affectionate
* weakness, lethargy, sleepiness
* head tilting
* unable to wake the cat easily when it is sleeping.
* drooling
* shivering
* staggering, uncoordinated movements, 'drunken' walk, wobbling, unbalanced
* ataxia - usually lack of muscular coordination, but maybe changes in head and neck movements
* disorientation (yowling, walking in circles, etc.)
* twitching
* stupor
* convulsions or seizures
* coma
If Jake has a combination of these symptoms, you can rub Karo syrup, maple syrup, honey, etc. on his gums. If you still have any of the canned food or even baby food (not with onions or garlic), you can mix syrup in and let Jake eat. If his behavior is better and his symptoms abate, then you know his insulin dose is too high. It's hard to manage hypoglycemia without your testing at home. Hypo can be serious. If the symptom picture fits with hypo, it may be best to take Jake to the closest ER vet where they can monitor and give dextrose intraveneously.
If you don't feel like your vet is managing Jake's diabetes well, if you post your city and state/province, there is a reasonable chance there is a member located somewhere near you who can offer the names of the vets they have had good luck with.
Re. the prescription food: Most cats hate the stuff. It's really junk. Fancy Feast, along with other canned, low carb foods are a far better option.
Janet & Binky's list gives you a selection of foods at different price points and the carb counts are noted. We typically consider low carb anything under 10%. If you switch to low carb, please wait until you can home test. Blood glucose numbers can drop quickly once you switch over.
See if you can find a product called Zero Odor. You may have to look on the web for it. It will help to remove the cat urine smell. Nature's Miracle is also a good product for this purpose.