At the age of 30, we just found out why my daughter has had a drippy nose and too frequent infections of the sinuses and upper respiratory. In her case, it wasn't allergies. It was vasomotor rhinitus. When I looked it up, it was fascinating and answers some questions about my and my sister's clear nasal drip that comes and goes -- and h;ow our worst times are those at the change of seasons. Examine this to see if you see a match.
Also know that tehre are scary things that can cause a cough so don't hesitate to ask hard questions. Like, could this be caused by any form of cancer or any serious disease. Make them think hard.
Also know that many doctors misdiagnose as they're in a hurry and expect you to come back if their suggestions don't work. Don't accept a "just live with it" diagnosis as it could result in a "just die of it" ending.