How can you tell if your stomach is bleeding from aspirin use?

Black stools: You will likely see black, tarry looking stools depending how much bleeding there is. However, if the bleeding is small, your stool may not change color and a physician would need to do a quick test which can detect microscopic amounts of blood. Also, you will likely have pain which can vary depending upon how severe the bleeding is and what else may be occurring (ulcers, etc.).