I've Had A Cough Now For At Least Two Months.

I've had a cough now for at least two months. I went to doctors when it had started and they told that my lungs were clear. I find that I'm always phlegmy and I seem to cough more when I drink. I describe like when you take a drink and it goes down the wrong pipe. I also have pain ( mid chest ) when I cough, assuming that's what as caused it. I did have sinus surgery in may and to open up the passages because I was prone to chronic sinus infection.