My son has been coughing for a few months now, but only at night. we went to the doctor a few times already and nothing seems to help?

What was tried?: I would say this is consistent with cough variant asthma. A trial of albuterol at night could be helpful in diagnosing the cause of his cough. I would want to know if he was having any other symptoms during this time (fever, runny nose, congestion). Does he start coughing if he were to lay flat during the middle of the day? A chest xray or perhaps a visit to a pulmonologist could be the next step.

Drainage/reflux: If this is only at night when he lays down you must look at other systems potentially triggering the cough.I see this in kids with GE Reflux or postnasal drainage with allergies.