The blood in the breast milk could be due to various reasons. If you notice blood within the first few days of breastfeeding, it could be because of the increased blood flow in the body supplemented with milk production.
If you have cracked nipples, you may find blood in the breast milk. But the cracked nipples will return to normal within a few days. If you find blood even after the nipples are fine, you need to consult a doctor immediately.