I have low blood pressure too (a good range for me is 70/50 but I've gone down to 30/21 while hospitalized) and I currently take medication to keep the bp up. You mentioned diarrhea - any chance you could have Addison's? Are you losing weight? Skin turning brown? Fatigue? Some things your doc can try : Proamatine, those lovely stockings (they push the bp to where it needs to be), florinef.