Did the vet test for an RI or just prescribe antibiotics? Did you have mucus coming from the snake?
Sometimes when a snake is getting ready to shed they will start having clicks, pops, or irregular breathing sounds caused by their loosening skin. I'm not saying that's what this is but it does happen.
Your snake will have a pink belly, then the skin will become cloudy which is the "blue" phase, then the skin and eyes will clear up and a few days later it will shed. At the first signs of a shed its usually important to bump up the humidity.