Help, my girlfriend smells like poop?

I've been dating a girl for a year now, and recently when we've been sleeping together in my bed I've noticed (I even got close and smelled one time) that there's a distinct odor of poop coming from around her backside. I really want to make the relationship work, but I don't know how to bring around any possible conversation to "so ... i've been smelling a lot of recently, do you have any thoughts about that", PLZ HELP