Three week old has a cold! Help

First time mom and I dealing with my three week old baby who has a cold. She’s been congested since birth, but yesterday morning she just wasn’t eating like usual . She’s slept most of the last 48 hours besides when I am forcing her to eat . She’s not eating nearly as much as she usually does. The doctor said I didn’t need to bring her in. To use Vick’s on her feet, saline solution and a vaporizer . All which I am doing . She’s not fussy at all. Just very lethargic and not herself. Am I over reacting ? Thank you! She sounds so bad and I can tell that she’s having trouble breastfeeding bc she can’t breathe correctly