Fading kitten syndrome

My kitten is three months old. And over the past two weeks he's been deathly ill. We managed to save him but not his brother. He is skinny and tiny compared to his sister (who is completely healthy) He has diarrhea, little appetite (we usually have to syringe feed him) and most worrying of all he has a hard time keeping his blood sugar up. Now his paws, ears, and nose are cold to the touch, even to my cold hands. When we took him to the e.r  four days ago he was wrapped up in a blanket underneath a heating pad. Should I do this with an ordinary heating pad on low? Will he die if I don't. Should I take him back to the e.r!? Please answer a.s.a.p another kitten death would be devastating.

Also can he even have Fading Kitten Syndrome at three months old? (I guess it would of started around 2.5 months)

Your kitten may be suffering from hypoglycemia. A stray kitten I rescued had those same symptoms. I found out too late that I should have been feeding him , via his bottle or syringe , every two hours(in smaller than normal amounts)... So , he became excessively dehydrated and passed away . I am so very sorry about the loss of the other baby and recommend seeing a vet pronto .

how much should I be feeding him? (if I feed him every 2 hours)

My understanding is that forcing him to eat too much could cause him to inhale the fluid. So, I would try to monitor the amount you give him calorically. What are you currently feeding him ? Are you using a powdered supplement?

Do you have honey or corn syrup? Giving him a small amount, on his gums or from off your finger, can give his blood sugar a small boost and help you to see if his blood sugar is dipping dangerously low. Additionally, I would research the food you are given him. Something in it could be agitating his digestive tract. Especially if he is still having diarrhea .

Get him to the ER vet immediately!  He desperately needs medical attention.

I am feeding him a.d critical care. 6ml in the morning and 3ml every 5 hours. The more worrying symptom is the coldness....I get him warm and then he gets cold again within the hour.

That's why he needs to get to the vet now.

Agreed. I think it's urgent.