After 50 some years of colds...

First I get way sicker than anyone else.
Second, I stay that way for a month or so.
Third, I wait for it to become a sinus infection
Fourth, I go to the doctor and get prescribed antibiotics

Somewhere at about 2 months it goes away.

Rinse and repeat several times a year.

The only thing that has ever helped me was Rhinocourt Nasal spray. But I don't know if that would help post nasal drip.