The neti and nasal sprays don't work well in the upper sinuses, because you are fighting gravity, and gravity always wins. The technique I developed uses gravity to get lots of saline in the upper sinuses. If you try it, make sure you use the hypertonic saline formula, which will shrink any swollen tissues and help with drainage.
Follow the directions about looking up and down after a flush to help get the remaining saline out. Some is inevitable, so always keep a tissue handy.
After about 2 weeks flushing maximum, walk around outside and breathe deeply through nose to repopulate the good microbes in your nose.
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.
Don't get miffed at your doctors. Some researchers recently did some DNA testing of the microbes in people's noses and found all manner of unidentified creatures, which indicates we know very little about proper sinus function.
If a flush doesn't work, then it's probably not an infection, try some different ENTs, maybe they'll have other ideas, like allergies or neurological.