My 4 year old daughter has had a cough at night for 2 years. (on and off) She will cough for hours on end. (1-4 hours) She seems to get a nasal drip and it irritates her throat causing this cough. She does not cough when she is awake. We have tried asthma meds., allergy tests, air purifiers, humidifiers, vaporizers, raising the head of the bed, antibiotics for sinus infections, cough medicines(over the counter and prescription) and we don't know what to do?? Maybe someone has had the same problem and can lend some advice?? Thanks