If other people can smell the odor, and you have no other symptoms of sinusitis, then you may possibly have an anaerobic bacterial infection in your sinuses. You can try a Neilmed Sinus Rinse, available on the internet, or a Neti pot. However, these infections are often in the upper sinuses, and regular sinus irrigation fails, because of gravity. What works best in this case is a Flip-Turn Sinus Flush, which defeats gravity.
http://www.medhelp.org/user_journals/show/2322
The Flip-Turn Sinus Flush is mildly risky, because you have to bend over to do it, preferably in a shower, but you can also do it outside on soft ground. Or, go to the comment I made on July 13, 2009 on how to do a sit-up method.
One of the last commenters (ihatesinusproblems) had little success with a Flip-Turn, until he put Grape-Seed Extract in the saline, which seems to have cured the problem.
Check out his posts.
Good luck, and don't give up.
friggy