I'm new to chickens but if it was normal then developed respiratory issues acutely then I would worry about possible trauma to the face due to the swelling associated with breathing. They can also develop pneumonia sometimes. The vetrx sounds like a good idea. Make sure it's eating and...
We got 3 rir chicks 1 month ago all are feathered out but this one ..... could it be a frizzle??? It is acting normal mayy be slightly smaller than the others though