What is the cure for sinusitis?

Antibiotics, a box of tissue, and something to spit in, like a small trashcan, to spit whatever it is that you cough up.

I would also try keeping a humidfier on to increase moisture, as well as using some vasoline rubbed on the inner part of your nose to assist with dryness. (If you don't have a humidifier, boil water on the stove to increase humidity)

Hope you feel better soon.

This is a serious answer , take it or leave it, mari-juans leaves in a tea.
my grandmother herbal cures, DRINK IT no Smoke it!
Antibiotics. I usually get prescribed Keflex or Levaquin because I am allergic to Penicillin.
salinex or salene and lots of fluid and nose blowing!
In addition to the previous advice, use a saline rinse in your nose and a mouth wash to rinse your mouth several times a day.
My wife has, well I guess had constant sinusitis problems. We move a few years ago and our new heating system includes a humidifier, makes a biggggg difference. If buying a new house isn't an option, buy your self a good quality portable one and keep it running while you sleep.

She also got this thing, I can't remember the name but I call it the nose tea kettle. It looks like a small tea kettle and she fills it with water and baking soda then puts the spout of the "kettle" in a nostrel and inhales the mixture. I know, it sounds quite weird but she swears by it.

Before you load yourself up on meds try to find other enviromental issues in your home/work place that are causing it. Diet and exercise can also be a factor.

Good luck.