Constant phlegm build up in throat (medicine?)

Hi all, for the past month or so, I've been having this phlegm build up in my throat. I'm 22 years old and I have been smoking casually just about everyday for the past 3 years. I feel like there is this ball of phlegm in my throat moving up and down, and every time I try to clear it by coughing is just seems to come right back. Its getting really annoying and sometimes to the point where i keep coughing over and over again till it hurts.
Sometimes when I cough some phlegm comes out but it doesnt do anything.

I have read about people with this same problem, and I got some good useful information, but no one replied with any medicine that could cure this problem.

I tried taking this chest congestion medicine and it didn't seem to work. I was wondering if there was any other over-the-counter medicine that I could purchase at a local drug store that would help my problem?

Any help would be helpful.

Thank you in advance.