Have you tested your blood pressure, hemoglobin, etc? Chronic diarrhea may lead to low blood volume and chronic anemia, which will further contribute to the shortness of breath. Of course, there are still lots of other possible reasons. Preliminary check-ups include a routine blood test, fecal occult blood, ECG, echocardiography, pulmonary CTA, etc. After these examinations, you may find out the cause.