If you google "CNN sinus infection" you'll see the study that proves what I've been saying for years--antibiotics don't work well against chronic sinus infections.
A Neilmed Sinus Rinse is the best treatment for maxillary sinus infections, but gravity prevents it from working in the sphenoids. Here is what does:
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, or perhaps a plastic basin or tub, with the shower running for steam.
Yes, I had the same problem and treatments as you until I invented the flush.