It could be that your baby has developed an intolerance to other things besides milk protein -- like wheat, eggs, or peanuts -- which are also transmitted via breast milk. Try removing these foods from your diet, one at a time, and see if you can narrow down the culprit.
If not, and your baby is still experiencing symptoms -- especially persistent bloody poops -- you should see your pediatrician. You might even want to bring a dirty diaper as evidence when you go in. He or she may recommend you see a pediatric gastroenterologist to rule out other problems like a bacterial or parasitic infection, an anal fissure (a tear in the tissues around the rectum from passing hard stools), or colitis (inflammation of the intestines, which can be genetic).
Copyright 2009 Meredith Corporation.