Anemia found on blood test. Low hemoglobin, hematocrit, mcv, mch, high rdw. Have had heavy periods for a few years but why would it just show up now?

It takes time to exh. We all carry extra reserves of blood and iron stores in our body which can make up for moderate blood losses for a long time. Only when the reserve is exhausted and there is no more iron left in the body will your blood tests start showing up Anemia. You need to ask your doctor for providing you the raw materials(like Iron supplements) to help you make extra blood.