My son just went through this and after six weeks of no sleep I went on the warpath with the cough and I won!
First, since the healing and stuff goes on at night, I did this regimen before bed. Second, I think that some medications for chronic type problems (like inhalers or nasal sprays) for children without chronic conditions create a cyclical dependence. So, here's my approach:
CONSTANT humidifer in the bedroom. Cool mist cleaned the unit daily.
Saline Spray/Flush before bedtime. Incredibly important to keep the stuff moving. What you flush out of the nose will not be draining down the throat at night and irritating that passageway.
Ibuprofen to reduce inflammation and stop the cycle of inflammation.
Little Coughs Honey Elixer. For good measure.
Saline spray also 1-2 times per day as needed type thing to keep the congestion moving.
Once he could break the cycle of coughing fits, the cough stopped altogether.
Good luck. Hang in there!