What Causes Persistent Foul Smell In The Nostrils?

I have, for three weeks now, had a horrific smell in nose while inhaling, every breath. No bad breath, no body odor. Only I in room of family or people can smell. It is repugnant smell, varies from a 4-10 on scale of 10. Like rotten flesh, dead animal in car heater, bad bowel movement, skunk, etc. mix of those. Also 6 weeks ago colonoscopy which showed some colitis after being totally clean 4 years ago. Smell from that problem? No sinus probs, massive blood work all show within normal range. Stools are negative on any problem. Horrific smell. thans