I agree with your doctor that uterine tumors (I assume fibroids) are
not causing the change in the color of your stools. Eventhough the
color is usually brown , many different kinds of foods that we eat
changes the color . For example if you eat a lot of spinach or greens
then you can have green stools. If you eat a lot of carrots, your stool
could be orangish. Beets can make your stool color red.
You might want to add some fiber supplement to your diet daily and
drink a little more fluids. Regular walking three times a week will
help. I am not sure where you got the idea of pedunculated tumor ?
Polyps or growths in the colon
or large intestine can cause bleeding etc.
Hope this would releive your concerns.
Wish you good health.