L.B.
I get canker sores in my mouth occasionally when I get sick. Immune system gets out of whack and that's where I'm affected. I use Kankaide, it's a topical med that you apply right on the canker sore and it numbs it and puts a protective coating on it. That post nasal drip can be a real pain. I would try a humidifier at night and let the cold run its course. Hopefully it's not allergies. If it is allergies you may try the claritin since it has a different active ingredient than zyrtec and you may have better results.