Re: Natural help for pollen allergy/draining sinuses?
Try something to wash the nasal passages out a few times per day, esp. after you've been outdoors. A neti pot (find at health food store) or a personal steamer (loosens secretions) can be helpful. While thinner secretions can translate to 'more' for a brief period of time after a cleansing, there will usually be less total throughout the day.
Reduce your exposure to the allergens as much as possible. If you have forced air, make sure the ducts are clean, and use a HEPA filter on your furnace. A portable HEPA unit w/99.7% efficiency, for small rooms like bedrooms & offices, can be purchased for less than $100 & these are worth their weight in gold. There is no substitute for avoidance of exposure to allergens.
You are vegan so no dairy, right? That's helpful. If you feel your allergies have morphed into sinusitis, (not uncommon, allergies mess up the immune system) you might look into an anti-Candida diet.
Sometimes people suffer exceptionally from allergies if sulfur is low in the diet. That's onions, garlic, or if you want a supplement, MSM will give you both sulfur & methyl groups.
Quercetins are nutrients (also found in onions) that can be helpful in quelling the allergic response.