My dd had blood in her stool when she was 6 weeks old and it continued until we went to an allergist and discovered she had a milk protein allergy. With the protein allergy their intestines get very irritated until they bleed. Often, I was told, there will be blood in the stool but it will not be visable so a stool sample is required to confirm blood. After that, they do blood work before and after milk is given to see if there is actually an allergy. My dd is now getting over her allergy at 14 months. At 13 months we gave her yogurt and cheese and she was fine but she couldn't take any milk. We finally started her on 2% milk which she was fine on, then we gradually cut it with whole milk and I will be doing a complete switch next week. Maybe try yogurt (high fat and plain, I use one that is 6% fat) and cheese to see if there is still a reaction?