I think i have a sinus infection. but how do i know for sure?

Sinusitis symptoms: Symptoms of sinus infections usually follow several days of URI or allergy symptoms. They include: nasal congestion, post nasal drip, thick & colored mucous, headache, fever, facial swelling, cough and increased facial pressure when bending forward. Diagnosis is often by history and physical exam, but occassionally CT scans of the sinuses are performed.