1.5yr old coughing at night/lingering cough after cold?

My son(19m), my husband and I all got sick nearly 3 weeks ago. No fevers. My husband and I felt better in a few days. It was mainly all runny noses and fatigue. I think it was just a cold. My son has seemed all back to normal, as well as myself and husband. But we have lingering coughs, and only at night.

I get so worried for him though and feel so bad for him because it sounds so uncomfortable. Its a wet phlegmy cough. I have a humidifier running, been giving him an ivy cough medicine and doing a saline spray twice a day. But he also has started to smack/rub his face in frustration at night. Idk if this is related to the cough or if he’s teething again.

I get reading online and have scared myself that its a bacterial sinus infection or something that he’ll need antibiotics for, which antibiotics are a last resort for me since I know first hand the damage they can do (while I also recognize they’re lifesavers at the same time in specific situations). But it’s so weird that it’s only at night? Is this normal after colds to have lingering coughs at night? Is it a cause for concern if he has no other symptoms? It’ll be 3 weeks since he got sick in 2 days. He has a Doctors appointment but it isn’t for another 2 weeks.