We Have An 8-9 Year Old Female Lab Has Been

We have an 8-9 year old female Lab has been very healthy. But in the past two weeks she has had a dry cough, like she's trying to cough something up or something is stuck. But when she does cough something up it is a white milky substance. We live in Albany Oregon and we always have a bad cottonwood pollen this time of year. But it never bothered her before. Do you have any ideas ?