I'd call the doc on Monday. This is not unheard of but should be evaluated. It's possible you just plain haven't processed enough stuff to be worthy of a poop yet. But better safe than sorry. Do you have any other distressing symptoms involved with trying to poop and not being able to? How about belly pain, distension, burping foul smelling/tasting stuff? Those would be things that would have me saying DO NOT WAIT GO NOW.