my dog has the above symptoms for 2 years now

vet says it's trachea collapse but x-rays show that the tracheas are in shape

he doesn't cough blood but from time to time, especially when the weather changes, he will cough and retch badly and somtimes cough out white mucus.

He coughs when excited and even when he drinks...

I am thinking of getting a kids' cough syrup since the vet says let it be...

other than that, my dog's health is very good and he's active and eating well for a 10 year-old shih tzu