I did anilingus with a guy a few times before & he tasted clean, the last time i did it it taste like poop and i can still taste it in my mouth, why?

Part of that may: Be the psychological effect of licking ; tasting feces. Feces are considered "unclean" by most. Anilingus is a sexual activity that many people find inherently "distasteful" or "disgusting" ; is often considered taboo. Do you have these feelings or thoughts? If not consciously - then maybe subconsciously? Anilingus can lead to infection from the feces as well as transmission of some std's.

Oral Anal Sex: Rimming is a common sexual activity. Some people really like doing it or having it done to them. However, one should not be forced to participate if they do not want to do this activity. You have the right to say no. Taste is caught up with smell. Have you cleaned your nose and skin around your mouth? If you have then this may be psychological in nature.