I agree with queen. You need to take the cat to a vet. Losing weight isn't good at all. Kittens are extremely susceptible to numerous illnesses. Their systems aren’t always as strong and supportive as we'd like it to be. Could be an upper respiratory infection, which needs tons of antibiotics and care. The snoring part makes me believe he's got the flu..badly. A lot of cats don't make it, so I recommend that you make an appointment as soon as you can or take the little one to an emergency hospital. I don't know of any home treatment other than keep him comfy, wrap him on a blanket and let him rest, and this will not solve his problem.
Good Luck.
I know how worried you must be. The kitten needs to see a vet ASAP, when a cat coughs and sneezes it never just goes away. How long ago was he on the antibiotic? Maybe, you could call the vet and tell them that you need something else. And, one more thing, was the antibiotic liquid or pill? If it was liquid antibiotic, and you used a syringe, you have to be very very careful and give kitty a tiny bit at a time, otherwise there's a chance they can choke. I was very paranoid about that with my cats.
Good luck and let me know how it goes!!