I came here about a month ago because I was unsure what was causing my constant coughing. In the end I ended up in the ED (coz it was a Sun night and I couldn't stand another night of no sleep) and was diagnosed with bronchitis. I still have the cough , not much better (definately not worse thank goodness) but with similar symptoms to you. Sometimes there's phlegm, sometimes not. Sorry I can't be of much help to you, but maybe you should see a dr just to get it checked out. Like Emily said the colour usually means infection.
Tc
irish