You can add your location or country in your profile. That can be helpful with questions.
There are a few active health cracks on BYC. @azygous and , @Eggcessive are 2 I know of. Maybe they have another or additional advice.
Personally I would give him some healthy herbal additives and acv/garlic in the water.
Do a health check on other problems that may play a role. Like lice, mite and other parasites, like visible worms in the poop.
If you cant find anything, just wait and see. If he heals without medicines he...
Can you give more info? Photo? Close up?
Intestines problems and sneezing are not the same.
How long is this going on?
What are the symptoms besides sneezing?
I had chicks once who were sneezing. They infected each other. Some got over it very quick. But one chick sneezed for 6 weeks and...