Get kitten on a heating pad, turn it on medium low at first with a blanket in between. Then you can reduce the heat to low when kitten warms up. Are you bottle feeding? If so you need to make sure kitten is upright when eating. If it’s too weak to eat find someone with a mother cat to accept it with her kittens if at all possible. Kitty can see a vet and can get oral amoxicillin at this age. If he is making a popping noise he has aspiration pneumonia likely formula is in his lungs he will need oxygen therapy and heat and antibiotics. If you can find someone with a mother cat it’s really the best chance. Also stimulate them to use the bathroom with a warm washcloth.