Blood in stool...
...Isn't brown. It's red, or it's black, depending on where it comes from. I suggest you see your doctor. S/he can likely do a simple stool test, called a hemocult, in the office to find out if it's really blood (i did two this week.
..One was, and one wasn't). Then, whether it turns out to be blood or not, your pediatrician can advise you what the next step should be.