I can totally relate to this! Have had major problems through both my pregnancies with constipation because my heartburn was so bad, took tums (which constipate you), then pooped rocks. Honestly, I would end up with a sweat mustache every time I went to the bathroom - it was a major event that took some serious time!
Even worse was pooping after delivery. I still had the left over constipation from pre-birth but now had stitches that were painful and that I was worried about popping. My mother gave me a succession of enemas before it finally worked itself out. Horrible memory!
This delivery, I will be sure to be absolutely dedicated to miralax and fiber in the weeks leading up to the expected due date!