What Causes Chronic Cough Producing Thin Clear White Phlegm?

I have a chronic cough that produces a thin clear white material. Some times it feels like I inhailed a gas that makes me cough. It coming from the middle of the right lung. Sometimes the cough comes on strong one after another almost chocking. Tast raw or metallic.Was eating Asian food and the vapors off the Wasabe filled my right lung like a chocking gas and caused a strong series of coughs.