Your problem isn't unusual. It's an anaerobic bacteria that may or may not cause enough congestion to register for an ENT. My best description when I had it was dogpoop and old parmesan. Some campers may smell it when they pull out an old tent.
A saline flush will remove it. First, go to the drugstore and get a Neilmed Sinus Rinse. This may or may not work, depending on how high up in your sinuses the infection is, due to gravity.
If it doesn't, the cure, should you wish to try it, is the Flip-Turn Sinus Flush, in my journal.
http://www.medhelp.org/user_journals/show/2322
It's risky, because you have to bend over in a shower, but you could also do it outside in grass, depending on your fitness.