Yeah, there are a number of conditions unrelated to your regular dental hygiene that can cause bad breath. In my case, sinus problems were a contributing factor. Diet can have a big impact, too.
But if you don't have any of those happening, go to the dentist and have your teeth cleaned, and then brush at least twice a day, floss (or, if you're like me and really dislike flossing, use a water pik), and use a mouthwash every morning.
The flossing/water pik thing can make a huge difference. You'd be AMAZED at all the crap stuck between your teeth that you don't notice with a visual inspection!!!
Cheers, Tim