My ferritin is 5, hemoglobin is in the normal/low range, and my periods are stopping. how is that possible? shouldn't they be heavy?

What are you asking?: Low serum ferritin usually indicates low total body iron, from heavy periods, from stomach cancer, from colon cancer, from a stomach ulcer, from hookworm, from ill-advised vegetarianism, or something else. You need to be under the care of a competent physician who's a good communicator. I'm glad you asked and this is a chance to explore -- answers in medicine are seldom so straightforward.