what causes post nasal drip and what can be done about it?

I suffered from post nasal drip. I was told it was allergies. It got worse and I started coughing all day. I went to an allergist and finally got diagnosed with vasomotor rhinitis. I take Astelin nasal spray and it has helped a lot. So, the nasal drip is caused by my reaction to chemicals, perfumes, smoke, etc.