The three main causes of low iron are—poor intake, poor absorption, and high loss. Poor intake can be compensated by diet rich in iron and iron therapy. Poor absorption is seen in conditions like Crohn's, IBS, severe acidity etc, and needs to be ruled out. High loss is seen there is a bleeding in your gastrointestinal tract, either due to esophageal varices, polyps, gastric bypass site, hemorrhoids or an ulcer. You should get your stool examined for occult or hidden blood to detect this blood loss. Also you need to get a pheripheral blood smear done to know the RBC count, structure and whether there is cytopenia (general decrease in cell count). The renal function and liver function needs to be checked, and electrophoresis of hemoglobin done to know whether there is thalasemia trait or sickle cell anemia. You need to see if there is vitamin B12 deficiency. Once the cause is found and corrected, then the lost iron is replaced by iron therapy, either in form of pills, capsules or syrups, or as injectable preparations. Consult your PCP regarding this. You should ideally consult a hematologist for this. Hope this helps. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.