My 2yo had a cold almost 3 weeks ago. after he recovered was told his lingering nightly cough was drainage. how long is too long for a cough like this?

A month: Colds and post nasal drip can linger for 3-4 weeks. It is also possible he has caught another mild cold after the last one and iyt looks like one long cold. I would have him rechecked. Sinusitis cod be a possibility and we often consider asthma with a night time cough...Elderberry can be helpful as can a.I.R. Tea (www.Franzcenter.Com under herbaceuticals).