Spring, 2013 and 2014, had a dry cough, every few minutes. Lasted about four months, no apparent cause. Only two things stopped it: Olbas Oil Pastiles and chewing dry cloves. I recommend both of these, the latter is an old folk remedy. When it went the cough literally stopped dead, from one hour to the next. I looked up and said to Mrs Scheduling "did you notice, I've stopped coughing ?"...and she said (etc etc).
This year have had a wet cough, tiny bits of mucas coming up. Suspect irritation from plant spores as we live in the middle of nature, rampant and wild.