If you don't have scarring, polyps, cysts or any physical anomaly, the best treatment for sphenoid or frontal sinus infection is a Flip Turn Sinus Flush to remove infected mucus.
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 you can kneel down and lean over a bathtub with the shower running.