This mat sound silly but a few years ago when I woked in a city centre I developed a dryhacking cough that wore me out and made my head ache. Nothing cured it. Eventually I saw a locum Doctor who said 't was an asthmatic cough - like asthma but coughing instead of wheezing. I still get it occasionally when pollen count is higher or air quality is poor (and if I'm in London in the summer). The cure was an asthma inhaler. Worth checking with Doctor. Hope it helps.
Try hot milk mixed with loads of muscavoda sugar (the really dark type) is very soothing on the through but not very good if your stomach is unsettled.