Weird health issue (not for the faint of stomach)?

Okay, so it's basically this. Lately, when I work out, or sometimes when I'm just lounging around, my /rectum whatever you wanna call it will itch. A lot. If I scratch it, even through the two layers of clothing I have on, then my fingers smell like crap until I wash them (usually immediately). But what's going on that I have itching down there that smells like crap? It's not like I'm defecating in my shorts or anything, and I'm not constipated and not seeing signs of diarrhea. Any idea what the heck is going on?