So my experience with DS2 was that we always suspected he had mild mpi, as a newborn and for several months he had very green, mucousy poops though no obvious blood, and he was a very fussy baby (had reflux as well). It was mild though and he outgrew it probably around 7 or 8 months and I started eating regular foods again, and around a year he was able to go to cow's milk. But during the early months he did always seem to be in a lot of discomfort which is why I eliminated dairy from my diet while BFing.
With DD I knew I'd be on the lookout for the same issues but she is now 8 weeks old and has been a very happy, content little thing. She eats well and sleeps well. Her poops have always looked like normal baby poops (unlike DS2's) and she never seems to be in any discomfort. She is gassy but passes it easily and it doesn't get trapped or cause any discomfort. I have her on probiotics which I think helps with that.
Today though she had a poop that looks very mucousy, which I really didn't think much of. But the next poop had what looked like some obvious specks of red blood. Now I'm not sure what to think? Like I said she is happy and sleeps well so discomfort doesn't seem to be an issue. Should I do something about it? Her next checkup is in 10 days.