air coming from my noise reeks... Ideas please

For the past few years or so, when I breathe out through my nose I've been getting a fecal odor. The odor is similar to the smell of my bowel movements, and it seems worse if I've been sweating a bit.

Is this a sign I'm not digesting properly? I've tried many different types of diets and fiber, nothing has seemed to help.

Thanks for any ideas.