sleep study postponed until January 2nd

[Crazy Free Spirit]

I could of already been done with my Sleep study but unfortunately it had to be canceled due to me being sick and still sick after two weeks at first I had a fever now I have Head and neck sweats and a bad cough that I cant shake off so I made my sleep study appointment for January the 2nd next year at 8pm.If I am not better by Monday I will make an appointment to see my Family Dr. to get some medicine that will knock this thing out for good it seems to want to linger on and on. What's the best medicine to buy for a severe cough? I have been taken tussin which only works for 4 hours and The generic Mucinex I need something stronger that works longer for at least 12 to 24 hour medicine so any ideas  would be appreciated thanks?