You must have internal bleeding.
What Would Cause Low Hemoglobin And Low Blood Pressure?
The Mayo Clinic website offers a list of causes for low blood pressure at www.mayoclinic.com
One possibility mentioned: "Lack of nutrients in your diet. A lack of the vitamins B-12 and folate can cause anemia, a condition in which your body doesn't produce enough red blood cells, causing low blood pressure." (Hemoglobin is the iron-carrying part of red blood cells.)
Of course these two conditions, of LBP and low hemoglobin, could be unrelated. But the idea of lack of nutrients does offer a possible connection: The lack of B vitamins would cause lack of red blood cells, thus a lack of hemoglobin.
Good luck!
One possibility mentioned: "Lack of nutrients in your diet. A lack of the vitamins B-12 and folate can cause anemia, a condition in which your body doesn't produce enough red blood cells, causing low blood pressure." (Hemoglobin is the iron-carrying part of red blood cells.)
Of course these two conditions, of LBP and low hemoglobin, could be unrelated. But the idea of lack of nutrients does offer a possible connection: The lack of B vitamins would cause lack of red blood cells, thus a lack of hemoglobin.
Good luck!