Anaemic, Vitamin D Deficient. Taking Iron Suplement. Having Headache, Short Term Memory Loss, Black Spots In Stool. Cure?

hello, I have bben found to be anaemic, I have been taken the iron suplements but on another blood test say 2 months later my iron levels are even lower, I feel really rires, have bad headaches , starting to forget the names of things. My doctor just prescribed me more iron supplements surely if they havnt been working thats stupid. I am also vitamin d deficient. Recently I have found I hae black spots in my stool is that normal and also how can I improve my situation the doctor doesn t seem to care?