well now that depends....it CAN be cleared up with saline spray and a humidifier if it's from allergies (but at this time of the year that's unlikely...most indoor allergens have peaked by now and the outdoor allergens haven't emerged yet), but I'm being treated for bacterial sinusitis right now and I'm on antibiotics....if it's serious enough that you're getting pressure or pain, and the saline drops and humidifier don't relieve most of the symptoms in a day or two, you need to go to the doctor you may need antibiotics.
try the home remedies first though...but if you're running a fever, straight to the doctor!
Allergy related most likely, use saline nasal spray and use vicks to help keep clear. it should help and go away faster also steam or a humidifier helps.