Your ENT gave you correct advice about the nasal irrigation--that is the most effective treatment against chronic bacterial sinus infection, but the shortcoming is gravity. You cannot squirt saline hard enough to get into your upper sinuses. Plus, the passages to the upper sinuses get swollen shut.
I had the same problem as you, until I developed the Sinus Flush, which uses gravity to get saline into the upper sinuses. However, it often takes several days of treatments to open up the passages to the upper sinuses. The hypertonic saline draws moisture from swollen mucus membranes, shrinking them.
Your ENT wisely didn't prescribe antibiotics, because they travel through the bloodstream, and there is no bloodstream to an infected mass of mucus in your sinuses. Read more here:
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.
However, if your sinus problems continue, then they are likely caused by the deviated septum, and a septoplasmy is the only way to correct it.
I did have a chronic sinus infection for 5 years, and I've had some acute ones since, but my sinuses are still clear.