I have read some info from some top LC specialist and they say that it is not true that a baby can be allergic to mother's milk. That there is no such thing. There is a possibility though that your baby could be allergic to any dairy products that you are consuming. It seems like your baby never had a problem with your expressed milk and then just recently has had this problem. Usually green stools mean a hind milk, fore milk imbalance. My second daughter had this problem. The pediatrician said the stools were normal but I didn't think so. So I worked on my daughter getting more of the hind milk in addition to the foremilk and the problem resolved. I nursed her for longer periods of time to make sure that she got the hind milk. I have read that this sometimes is a problem with women who have an abundant supply. The milk comes out so quickly that baby gets a lot of foremilk rather than hindmilk. It sounds like to me that since baby was just starting back at the breast again, that he probably got less breastmilk than normal and then possibly got more of the formula. Many times babies can get blood in the stools from formula. The cows milk that is used to make it is often times very hard on the baby's intestines. My one twin had that happen once. So I would stick with your gut instinct and keep doing all that you can to give your baby breastmilk. Pediatricians are not trained in lactation whatsoever. I would see a top IBCLC before I would ever believe the pediatricians advice in how to handle breastfeeding issues. You could even contact Dr. Jack Newman. He is wonderful and will answer your personal e-mails very quickly. Keep hanging in there. You are doing great. Let us know how things are going.