3 month old w/ a cold?

My 3 month old has a pretty rough cold. My 14 month old just got over croupe and I think my 3 month old has it now. I took her to the doctor yesterday and all he told me to do was use saline drops. She hasn't had a fever but when she coughs you can tell it hurts by the sound....she will just burst out crying for no reason. What should I do? Her doctor told me to contact him if she has a fever or starts vomitting.. but she has done neither...But I don't like this cough. We don't have a humidifier but we do have a vicks vaporizing mister....any suggestions?