I've got 'acute chronic sinusitis' myself ...so, on a personal note ...go with medicine =( ..keeping in mind that a sinus infection not only can get very painful and smell and taste weird, but can lead to pneumonia. Unfortunately, just treating sinus pain and pressure is not enough.. you'd need antibiotics.
naturally... ..I dunno the homeopathic or herbal remedies, there may be some. ...ehh... you might want to google "homeopathy sinus infection"? ..but as far as dealing with the pressure and pain, it's suggested to soothe the sinus cavity in any way possible. Taking a steaming hot shower, or breathing in (through the nose) the steam off a large bowl of hot (boiling.. but be careful, of course) water ...with a towel overhead to trap the steam ...will help the pain. But the infection will probably linger.
And try to expel any mucous-y goodness. It's infected and the greener it is, the worse it is =p ..apologies for the graphic image
best of luck