My son has been coughing & has phlegm for about 3 weeks. could it be he is allergic to my sister in laws cat? is that why he hasn't gotten better?

Pediatrician : If your son has had a productive cough for 3 weeks he needs to see a physician. With a history of prematurity, the most important concern is to have a physician fully examine, listen to his lungs and ensure he does not have pneumonia. If he has a fever you should bring him right away. Allergy testing referral can be addressed when you see the physician and HEPA filters are very helpful. Good luck

Maybe: Kids with minor respiratory viruses may cough for a few weeks. This can be aggravated by any of many irritants/allergens. Dust/smoke/fragrance/ cleaning fumes/aroma from laundered linens can all act as non-specific triggers. If the kid functions fine otherwise,eating and playing well without fever, you can monitor these issues at home.If he is acting sick, have him seen.