Humidifier is probably the best thing. Also try folding some little blankets for a little pillow while their sick for better airways. The doctor really won't do anything about it ,don't want to give newborns medicine. Let this be the first of many many sicknesses even before their 1st birthday, its good for them, don't worry.
Try using a humidifier while bby sleeps. Def keep bby bundled up nice and warm. Hopefully you can get an appointment asap.