How can I get rid of a sinus infection quickly?

Improve drainage. Sinus health is all about drainage. Remove the thick, obstructing secretions with salt water rinses, take Pseudoephedrine or use oxymetazoline spray for a few days, and get an antibiotic if you have greenish secretions. The best thing to do is to see an allergist to see if allergies are the underlying cause, and to learn what to do to control the allergic inflammation as best as you can.