Has any doctor discussed the possibility that you may have acid reflux, aka GERD? You don't even need to perceive the feeling of heartburn to have it--especially at night, when the acid backs up out of your esophagus as you sleep and irritates the vocal folds. You wake up full of phlegm that persists through the day (you misperceive it as catarrh or postnasal drip), which is your vocal folds' way of trying to protect themselves against the irritation of the acid. I had a very cloudy tone and lack of "edge" to my voice, which sounded tired (not rough, just like there was "no there there," to paraphrase Gertrude Stein). I sought out a teacher, who sent me to a singer-specific ENT (who also treats the members of the Lyric Opera). He 'scoped my folds as I sang and confirmed a moderate bowing on one of them--and on the photo, pointed out some irritation. He prescribed a "proton pump inhibitor" (in my case, Protonix, but you might be able to get relief with an OTC brand like Prilosec) to be taken at bedtime and again with breakfast. (The bedtime dose is more important, because you're lying down and need to fight gravity to keep from pickling your cords in stomach acid). He also suggested eschewing bedtime eating, and elevating the head of my bed, as well as instructing my teacher to prescribe exercises to build up my lower register. Three years later, my voice has cleared dramatically. (However, I do notice that when my Protonix 'scrip runs out and I have to make do with Prilosec, I get phlegmy again).

Oh, and I don't now and have never smoked.