Freaking out

My one year old had croup a week before my baby was born. It’s been about 5 weeks and now my one year old has a cold with a horrible cough. Long story short now my newborn is sick with a cough and runny and stuffy nose. I’m freaking out because his cough sounds horrible and I’m upset my 5 week old is sick. He dr said to have him come in immediately if he has a fever, which he doesn’t. I’m still worried, what else can I do ? How do I know his cold didn’t turn into pneumonia ? You would think the dr would take it more seriously that my newborn is sick but I guess it’s not a big deal as long as he doesn’t have a fever ???