I have had a very sore throat with almost constant flem for 23 days now. Mussinex D helps a little- a lot of post nasal drip night and day. How do I get rid of the flem which I believe is causing the throat irritation??

It's time to see a doctor who can prescribe something more powerful for the phlegm and make sure the worst is over. You don't want this infection to begin wandering around in your body.