Actually, you may have a sinus infection, possibly a fungus. Sinus rinses only reach the maxillary and ethmoid sinuses, the lower ones, because of gravity. Antibiotics may have no effect on infections in the sphenoid and frontal sinuses because of the lack of circulation, and they won't work on fungals very well. I had your same medical-proof problem for years until I developed the Flip-Turn Sinus Flush. It's risky, because you have to bend over in a shower to defeat gravity, but you are young.
http://www.medhelp.org/user_journals/show/2322
Try this for a week, and if you see no results, then go back to as many ENTs as possible until you find the one who knows what else you could have.