If the CT scan was years ago, I agree with Dr. Anthony, go see an ENT specialist.
Nasal irrigation works very well against blocked sinuses, but not the way most people do it. The neti pot, to me, looks like an invitation to a Eustachian tube infection. A better device is Dr. Mehta's Neilmed Sinus Rinse, available at most drugstores.
Unfortunately, it only clears the lower sinuses (maxillary and ethmoid) before gravity takes over.
I invented the Flip-Turn Sinus Flush, which uses gravity to flush out all of the sinuses. It's extremely effective, but it's risky, because you have to bend over, which could possibly make some people dizzy and fall.
I only advocate it if people have tried everything else short of surgery, or if they are young and fit.