I've been dealing with a dry cough for the last six months, and it's really starting to worry me. I've tried more than 10 different cough syrups, but nothing seems to work. It gets so bad at night that I can't sleep because of the coughing. What's strange is, I don't have a runny nose. Could you give me some advice on what might be causing this and how I might be able to treat it?