You already don't feel your best, and then you notice (or someone mentions) that you have bad breath. Did you know that bad breath can be a telltale sign of a sinus infection? It’s true. That’s what happens when you have sinus drainage in the back of your throat. It’s not pleasant, but it is treatable and when the infection is gone, so is the bad breath associated with it. Here’s what you should know and can do.