Coughing and HFMD

My 4 month+ old son has bad cough and lots of phlegm back his throat. Night time is worse. Plus its almost a month so we bought him to A&E cause this first time mom so dead worried. The doctor say his lung noisy and prescribe him a Salbuair Inhaler with mask and give him. She say its not for asthma but I google almost answers show asthma. I worried he have asthma. On top of that she give him nasal decongestion . I feel like he so young to given any medication and I dont him to depend on medication. Is there mummy out there whi has same problem or any suggestion? Im in my dead end. My daughter on top of that her hfmd rashes break out badly suddenly. And she also now start coughing but not has bad as her brother.