You might want to try bring the kitty in the bathroom. Close the door and turnthe shower onto hot. Let the steam build up in the bathroom. Kitty will get a little wet from the moisture, but it might help add moisture to his septum and also break up any congestion he has.

Little Noses are great. I use them whenever my cats get a URI. You might want to ask the vet about Zythromax. It's a pediatric antibiotic that really works well on cat URI's, speaking from personal experience.

I wouldn't wait too much longer before I take the kitty to the vet again. The last thing you want to do is have it turn into pneumonia.

Please keep us posted on your kitty's condition.