My kitten is still sneezing!?

Sneezing can linger for a long time, even after antibiotics! Mainly b/c it is viral in nature and antibiotics arent specifically for viruses. I wouldnt worry too much, sounds like you've done everything you can. If he gets any worse he will need to go back, it can become lethal to a cat when it spreads to the lungs. You would know if the kitten had reached this point, he would be lethargic and not wanting to eat or drink. I would just keep monitoring the kitten, and taking it to the vet for checkups. I think there are other tests they can do to confirm that it is a virus, such as taking swabs of the nasal page. But im not for sure. Normally these things subside slowly over time.