Sounds like your doctor made a correct diagnosis, but the treatment doesn't always work. You may want to give a Neilmed sinus rinse a shot, then go see an ENT for treatment, and if that doesn't work, this usually 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.