The odds are that it's hemorrhoids or something equally minor. 15.7 is really barely positive and just means there was a little bit of blood in your stool. A lot of things could cause that, the most likely being something like hemorrhoids or a fissure or something. Given that you saw blood, this doesn't even tell you anything you didn't already know.

When I was 40, I had rectal bleeding, some weight loss, trapped wind and occasional loose stools and the consultant said that if my mother came in with those symptoms, he'd be worried about cancer but that at my age, it was the least likely option and I'd be "the unluckiest person in the world if it turned out to be that."

Given that you are even younger than me and that the changes started with your having a baby, I would imagine the odds are if anything even lower for you.

Of course, anything is possible but there are so many possibilities - an infection, hemorrhoids, a fissure, a polyp, Crohn's, ulcerative colitis...