Rectal/groin odor (what is the cause of it)?

I smell a stool odor from my groin/rectal area. I have a good hygiene and the smell seems to be noticeable when I’m in a car with the window down or when the heater/ac on. I went to the doctor and they didn’t find anything wrong with me. No fissure or no hemorrhoids. So what could be the cause for the stool/rotten egg smell? 25 year old male