Making sure you are drinking enough water helps a bit too. Drink until you are peeing every hour and it's clear. After a couple of days your body starts using the extra water (thus the pee breaks decrease) but your mucous is still thinner and easier to cough up.
I find a humidifer helps me a lot as well.
Welcome to the asthma community!
There are many causes for post nasal drip, as you know allergies is one of them. But sometimes it's related to structural problems in the sinuses/nose region. A deviated septum or scar tissue from sinus infections can create poor drainage problems. Certainly eliminating any allergy exposures will help. Have you thought to try to irrigate your sinuses with a salt water solution a couple times per day. It's work, but it does help cleanse the extra junk out of them. Also some doctors will prescribe a steroid nasal spray, to help reduce the inflammation, which in turn helps to reduce the mucous production. It is something to be considered, after all quality of life is important. And when symptoms become unbearable, then one has to step up the treatment plan.