Oh! Didn't see the part about the stuffy nose - sorry! Sounds like Tetracycline should work - that's what the feed store recommended to me when I thought I needed it. Good luck!
I wouldn't cull that chick too soon - sorry! As I said in a previous post, I had one chick that did the gaping thing for about a week. I separated her from the flock, put antibiotics in her water (and the flocks - followed advice from the feed store) and didn't expect her to live. However...
I had a chick that kept opening and closing its mouth and called the breeder who suggested it was because she was the smallest, it was probably getting packed on the bottom of the chicken pile and was gasping for air! I didn't think this little one would live, but now I believe the breeder was...