For anyone who may come across this, the wet anus + odor problem is really common in fbo sufferers. I believe this is either 1) regular sweaty butt but mixed in with bacteria from stool causing the fbo or 2) probably more likely if suffering constipation or diarrhea issues - anal leakage. Anal leakage can happen to anyone but more likely if you have an anal fissure (literal cut in the anus allowing things to leak out), hemorrhoid, or more common ailments like constipation and diarrhea. Diarrhea is usually fishy smelling too so if this happens often and it alternates between fish and fecal odor - don't write it off as tmau just yet - it's probably leakage. Hopefully kegels and baby powder in the area will minimize the smell.
You might have a GI doctor check to see if you have an infection or something else causing your symptoms. He/she should ask about your bowel habits and what your feces look like (is there blood, what color, how much a day, how many times a day, formed, loose, etc.).
You might also have a doctor check into your lack of scent detection with your nose, to make sure you don't have something causing a decrease in your ability to smell.