I have been through the same. I’m highly allergic and postnasal drip has always been a constant companion. I have tried saline nasal rinses and what not, but to no avail. Finally, I was given a scrip for Ponaris® by my ENT. Initially, I had trouble in locating pharmacies that actually sold it, since it was not so popular. Luckily, Rite Aid had it. Got it and used it, and must tell you… it really works!
Since I was very curious about Ponaris®, did some background check and found it helps not only fighting postnasal drip, but also congestions caused by cold (sinusitis), atrophic rhinitis (all three types, acute, allergic and chronic) allergies caused by hay fever and rose and mucosal encrustations.
Looked up for ingredient details and found this: Ponaris is iodized blend of oils of peppermint, eucalyptus, pine and Cajeput in cottonseed oil base. The total iodine content varies from 0.4-0.6% by weight.
I also added Ayr-gel with Ponaris® since they complement really well. This can be applied with a Q-tip inside nostrils, won’t go down the throat or leave a bitter taste. Ponaris® before going to bed and Ayr-gel in the mornings and evenings. It has worked out very well for me, hope it does the same for you. Happy sleeping.