Haha the same thing has happened with me. I don't know what position my boobs will be in from one day to the next. It's always popping out of E's mouth.
E tends to chuck little tantrums when she has a belly ache. She uses my boob for comfort and to help push her poo out, but she usually sucks a couple of times, screams, sucks, screams, then eventually she eats then does an epic poo!
Maybe she just has wind or a sore belly or something. It's hard when you don't know what's wrong though hey.