I've just started ferrous fumarate as sulphate didn't suit me. i'm feeling quite poorly, my iron stores are 4 is that low?

It should help: The ferrous form of iron is usually the best absorbed. Some people tolerate ferrous fumarate or gluconate better than ferrous sulfate. GI side effects are usually the problem. I presume your ferritin level is 4 ng/ml, which is low suggesting iron deficiency and is the likely cause of feeling poorly. Hopefully you can tolerate the ferrous fumarate and resupply your body's iron.