I have suffered from sinus congestion, inflammation and pain for a long time. Recently, I have started using a Neti pot every day, without fail Though it may sound like a lot of work, the following routine has bought me considerable relief.
First, I fill the Neti pot with luke-warm, filtered water. To this, I add a teaspoon of Sea Salt, and a drop or two of edible Peppermint oil. I irrigate with that until pot is empty. Then, I drench a washcloth with very hot water, and hold it over my eyes and sinuses, while leaning over sink, gently exhaling through my nostrils. Usually some remaining saline solution will drip out. I then blow my nose very, very gently, for I have found that water will back up into my ears if I'm not careful. After that, I brush my teeth, and then gargle with salt water. At this point, there's a lot of post nasal stuff draining into the throat, and this kills the germs and allows you to expel them.

And last, but MOST IMPORTANT, I've been taking two capsules of Oil of Oregano daily. This has successfully killed that foul odor that was coming from my nostrils! I also abstained from sugar during my two weeks of the above routine, because I had a suspicion that since the odor smelled moldy, I might have to destroy actual mold in the sinuses, and didn't want the sugar to defeat this. Hope this helps!