Once you have the infection, you need to cure the infection before any sort of rinsing will be truly effective and useful. I, too, have chronic sinusitis and the normal antibiotics stopped working for me since my body became "immune" to amoxicillan, which is the most commonly prescribed antibiotic. So, it wasn't working. They switched my antibiotic and amazingly enough, the sinusitis cleared up! Now that the infection is gone, I can maintain clean and clear sinuses using natural methods and hopefully keep the sinusitis from recurring.
An infection is an infection and without real treatment of the infection and killing of the bacteria, the bacteria and infection can spread into much worse things that require real hospitalizations (I've heard of sinus infections spreading into the brain tissue that is quite close to the sinuses; I've also heard of sinus infections spreading into the blood stream). Think of it this way, there's a reason the life expectency was so low before the discovery of penicillin! People died from everyday infections that were only treated with natural remedies, since there weren't antibiotics yet. Modern medicine isn't bad when used appropriately and as necessary. Then maintaining your body as naturally as possible can hopefully keep worse things away, but you've got to take care of those worse things if they do occur.
Good luck and feel better!