My drs tried not to put me on antibiotics unless they were sure it was bacterial, hoping to avoid some of the resistance that we already deal with. The snotty nose definitely can come along with Fifth's, so that one I'm not sure about. The only thing I can think of, is they are hoping to keep her from secondary infections? I know when I've had a couple viruses that were known to be nasty, I was given antibiotics in hopes that it would help fight off secondary infections.