Q&A: My Baby Has Blood In Her Stool — What Do I Do?
Blood in baby's stool is almost always associated with a cow's-milk allergy (bovine protein is the culprit). Thing is, that bovine protein can take up to two weeks to leave your system, so give yourself a little more time. Be sure to read all labels, and watch out for ingredients like "whey" and "casein" (both come from milk).
The other foods you've been cutting out are common allergens, too, so keep ditching those for these two weeks as well. (About one third of babies who are sensitive to cow's milk are also sensitive to soy.) If the blood disappears, you can try working them back into your diet one by one.
Some experts also think that blood in the stool is caused by the malabsorption of lactose. They say that slowing down digestion — by making sure baby takes plenty of your fatty "hindmilk" (the milk that comes at the end of feedings) — can help solve the problem. To test this theory, you can try limiting baby to one breast per feeding for a while, so that he stays on long enough to get the fatty stuff. It may also help to express a bit of your foremilk before baby latches on so that he gets to your hindmilk sooner.
Make sure you doctor also checks baby’s stool for infection and parasites.