Ok first off I would suggest modifying your diet. It could be an intestinal bacteria. Are you sure you don't have any symptoms? Not even white coat tongue, post nasal drip, blocked nose, fatigue,, trouble breathin, anything?
You could start a candida diet, which is void of Sugar completely to starve any possible fungal infection that could be causing the odor, and your bowel movements are completely regular? that's strange.
Or it's a possibiltiy you gave tmau, how pungent is the odor?