How can i relieve sinus pressure after using a decongestant that isn't working?

Saline: Try using salt water nosedrops or the netti pot.And call your doctor.

Sinus pressure: You have to help the sinus openings get wider so that the air pressure or mucous build up in the sinus can get out. In order to do that, u have to know the cause. But if the cause is a cold or simple allergies then taking advil cold & sinus, Mucinex (guaifenesin) d, or afrin nasal spray briefly, can help.