9 1/2 month old with night coughing?

My son had a cold about a week to week and a half ago and has really gotten over it, but for some reason when he wakes up for his night feeding (between 2-4 am) he will eat and then cough for around an hour (sometimes longer) and then go back to sleep, it's kind of a phlegm cough. I called the doctor today and she said that if it happens again tonight to call tomorrow and come in. I am just wondering if anyone has had this experience? Could it just be from him getting over the cold? He doesn't do this during his naps during the and he doesn't really cough too much during the day, just here and there..any ideas?