What's the difference between a sinus headache and a sinus infection? i've heard the term "sinus headache" used frequently.

Not the same thing: A sinus infection is when you have bacteria or viruses in your sinuses and your body has been invaded and has to defend itself against 'germs.' a sinus headache may just be due to swollen sinus tissues which can happen from drinking milk or using other dairy products, (most likely, and you should try quitting all dairy for 10 days or 2 weeks to test this), or from overreaction to pollen and similr.

Not always sinuses: The term sinus headache is way overused. In fact, many "sinus" headache patients have completely clear sinuses on scans.. Meaning it never was coming from the sinuses! migraine is a missed diagnosis in many such patients. If you have sinus infection there is often facial and/or dental pain, nasal drainage, congestion, cough, bad breath, fever etc. If it's just pressure, it is headache.