there is a difference between blood IN the stool and blood ON the stool. can you tell which? usually blood IN the stool is a darker red - black, as it has been digested. This could be blood from you, if your nipples are cracked, for example (although I doubt at this stage that would be likely), or from baby's gut. The allergy or sensitivity as pp mentioned could also be a cause.
Blood ON the stool is bright red, as it has not been digested, and is usually due to an anal fissure. These are nothing to be concerned about, will go away, and are most likely due to the increased bowel movements or straining.
Green poop can be caused by a virus that the body is trying to process. The green color results when the body digests more quickly then normal.
It is definitely worth analyzing any new foods you have eaten, as well as your regular diet, and possibly cutting some out for a period of time.
hth!