I used to suffer from pollen related sinus infections every year back when I lived in Atlanta, which happens to be the pollen count capital of the world (the flowers sure do make the city gorgeous each spring, though!).
I finally went to a good local ENT doc there, and this is the regimen that helped me: Sinus infection causing bacteria tend to thrive in low oxygen scenarios, which clogged, mucus-y sinuses are the manifestations of. The bacteria bloom under and within blobs of mucus, caught in the little dips and crevices within your sinus membranes, that have become stagnant and thickened by dessication as your breath passes over them, making them thicker and allowing the anoxic bacteria to continue thriving. Pressure pain and inflammation pain comes from that process.
Take a decongestant medication that stimulates fresh, watery mucus production to dislodge and flush away the stale muck in there. Drink plenty of water while the pill is in effect, over the course of four to six hours. It's messy, you'll have a runny nose and sinus drainage into the back of your throat. Lots of hacking and spitting. While sitting in a steady chair, tilt your head and face slowly in different directions, especially dipping your head all the way down to your chest, then all the way back as far past your shoulder blades as you can manage, then tilt left as far as you can, then right etc. etc. to allow gravity to work in pulling some of the gook loose to where you'll cough it up and it drains more from your nose as well. Go slow, because that shit is thick and gooey - takes time to start sliding loose. Do that bit a few times an hour for 3 to 5 minutes a session.
After this miserable phase opens things up a little, and you can actually breath a little through your nose, use a sinus flush bottle you get as a kit at the drug store to very gently fill and flow out your sinus cavities with warm sterile saline solution (eyewash saline works fine, too). After that flush, you should be able to use a nasal inhaler, like Flonase, to maintain the sinus airway open.
