Given that none of the normal things are working - it could be whooping-cough. In that case, plug an electric kettle into the bedroom and keep it boiling - the steam helps (my daughter had it at about the same age - it was a bad time as the other had measles). You can also try hot milk and honey, which lines the throat and helps a bit. If it is whooping-cough then you just have to live through it. Is she/he looking a bit alarmed at the onset of the coughing session? Eyes wide etc.? If it gets worse, call the doctor, but mine both survived OK.