I can attest to this advice. I suffer from sinusitis multiple times a year and when I was thinking I was going SF I would continue training and running a lot while my post nasal drip transmitted the infection to a sore throat, to bronchitis and once to pneumonia. Rest is best!
I have found this device (
http://www.hydromedonline.com/ ) offers me some decent relief when used daily when I feel sinusitis begin, far more than any OTC decongestants etc etc.