Have you taken him to the vets as it could be cat flu, the symptoms are, Intermittent sneezing, watery mouth with saliva running down the chin, runny nose and eyes, quiet and lethargic, loss of appetite, and a cough or loss of voice
You can try the human trick of Vicks or Olbas Oil in hot water near him...if you have a cat box for taking him to the vet you can place the water outside of it and cover it and the box with cat in to allow the vapours to reach him without any danger of the water burning him...
The vet recommended this when my cat had cat flu last year
You should take your cat to the vet asap. but until then, the best method to give your cat some relief is to put him in the carrier as suggested and put some vick or carvol capsules in steaming water. Cover the bowl and carrier with a bath towel. It sounds like your cat needs an antibiotic.