In the 80s, my mom took me to our physician because I was complaining of stomach pain. He asked me if I was under any stress (oh yeah, I was!) and then suggested I see a psychologist he had in his office.
He said my pain or discomfort was a stress related thing. I've since learned that belly pain can indeed be caused by anxiety. My psychiatrist said it has to do with the vagus nerve-to-brain connection.