off topic: fb posts seen by my friends

i have turned on every privacy setting i know and update them every few weeks but FB has its sneaky way of letting my friends know (comes up on their feed) what i post on groups i join (even though some are and some are not in the public and closed group i joined). can somebody tell me how to turn off those settings (if such a thing exists in fb lol)? i'm sick of friends poking their nose into my questions/ seeking advices on social groups i join.