How does he look? Is his breathing labored? How do his eyes look? Are they closed or half closed much of the time? My limited experience with respiratory infection in hatchlings is that you can really tell because they look really bad. The way you describe him, it sounds like you may be worrying about nothing. If he's eating and seems fine otherwise i wouldn't sweat over it.
Remember the words of John Prine:
"quit wishing for bad luck and knocking on wood"