You mentioned you just stopped breastfeeding, did you go to formula or cow's milk? If you went to formula maybe she is sensitive to the kind you got, maybe you could switch to one that has the proteins broken down (carnation good start). If you started cow's milk maybe she is not quite ready for it. Also even though it makes you feel like it something real serious since there is blood there could be a simple explanation. Occasionally, baby may spit up forcefully and tear a tiny blood vessel at the end of the esophagus. This also heals quickly. If it continues on for more than a week I would get a second opinion, especially if she has other symptoms along with it.