Two things I did when I recently had a sinus infection and was desperate to get rid of it w/o abx (and did!) was to swab inside my nostrils with a paste of a little ground cayenne pepper + water with a qtip & take a big sniff to get it into your nostrils. It does burn for a few moments, but it is tolerable (at least for me). It was a home remedy I found online and it definitely clears your sinuses so you can breathe for a bit. Also, drinking a "tea" with hot water, cayenne, 1/2 a lemon + raw honey also helps clear your sinuses.
I also did much of the immune-boosting things already mentioned. It took a couple of weeks, but I beat it without an rx.
And I used a grapefruit seed extract nasal spray, b/c my nose was so dry.