Phil,
I agree with CJ, allergies are a prime suspect. Pollen is high in many regions right now, record year for us here too.
... are you eating at all by mouth? If so, maybe residue is pushing up via the weak soft palate into the sinuses... just a thought. No, no sinus infection for me in many years, but when I eat or drink my nose tends to run. It varies as to how much.