Low ferritin

33F

I have low ferritin of 7 and have for a while. Hemoglobin normal, iron 55, tibc 399. so it’s iron deficiency without anemia. I’m trying to figure out why I have this. I have no energy and feel faint sometimes. I do have heavy periods a lot of the time. I am taking iron tablets for 2 months now. I am trying to heal my gut. What could be the cause?