Smelly brown substance under stomach

Im a big girl not gonna lie, and bein a big girl means I have a big stomach. So I just showered yesterday so I know I’m not dirty, but my stomach crease between my stomach and vagina smells REALLLY bad🤢 and It was really moist, and I wiped it and brown was on the tissue, I kept wiping it until there was no moisture or no brown left, and it still smells. I didn’t exercise at all today, or yesterday so I know it’s not sweat. What is it?!