I too have suffered severe post nasal drip after having COVID. Try Standard Process (a brand) Antronex. It is a liver detox supplement. When the liver has trouble detoxing, it exacerbates symptoms in the sinuses. I’m a small person, 125 lbs and I took 3 tabs morning and evening until my symptoms were much better (a couple of weeks), then tapered down to just 1 to 2 once or twice a day. This was a MIRACLE worker for me, my symptoms are 90% better, I can now sleep at night without sinus issues. They have a bottle of 330 tabs for $48. You can go to their website and put in your location information and it will list local locations where you can buy this. Please give it a try and post your results back to this list. It worked so well for me, I’m curious to see if it works for others.