Sounds like an upper respiratory infection you may want to take him to the vet to be treated before he gets worse
Could be cat~flu. Very contagious to other cats so keep kitten away from any other pets until cleared up. Will need vet treatment and antibiotics, along with isolation until well. Make sure you keep kitten vaccinated for at least the first 3 years.
Did you get your kitten vaccinated? You should take her to the vet. There are a number is illnesses a kitten can get with these symptoms. All of which need to be treated.