Anemia could be caused by the following:
1) Heavy periods and/or bleeding
2) Deficiency in b12 (low stomach acid, vegetarian/vegan/raw diet, parasites)
3) Imbalance between the minerals - iron, zinc and copper.
Before buying any further supplements, I would recommend you buy yourself a hair mineral analysis. It's only about £50. This will give you a graph of the mineral imbalances and make recommendations on certain lifestyle changes, diet and supplements which help support your body's ability to absorb the essential minerals to bring balance. It might not be simply a matter of taking iron. You could be high in zinc, and zinc competes with iron. You could be low or high in copper etc.
Note: Copper supplementation can be dangerous if you are in fact NOT low in copper.
1) Whats your blood type? Blood type O suffer more inflammation, and lose more blood during periods due to thinner blood. If this is you, then consider taking adding both meats and dark greens rich in vitamin K and calcium to your diet - spirulina, kale, wheatgrass, thyme etc to aid clotting.
If you are blood type A, then consider taking fish oil and vitamin E to help thin the blood. If you are taking calcium then stop. Get the hair test. Calcium supplementation can also interfere with the iron/zinc/copper balance as well as cause digestive problems.
2)A deficiency in b12 is indicated by low stomach acid, or eating foods which reduce stomach acid and/or eating a strict vegetarian diet. parasites
like 'tapeworm' can also prevent absorption of b12. Before you start taking b12, look into the different types of b12 that exist. Cyanocobalamin is been claimed to be created using cyanide. I can't clarify this, but methylcobalamin, though more expensive is much more absorbable and you can buy it in large shot doses. Also consider eating more meat, because this will encourage more stomach acid production therefore aiding the ability to absorb both iron and b12.