In addition to the copper that Chirley mentioned, B6, folate and B12 are needed in the production of hemoglobin.
Your chemotherapy may be responsible also. Either directly or indirectly by depleting some nutrients.
Marlene, wife to John DX w/SAA April 2002, Stable partial remission; Treated with High Dose Cytoxan, Johns Hopkins, June 2002. Final phlebotomy 11/2016. As of January 2017, FE is 233, HGB 11.7, WBC 5.1/ANC 4.0, Plts 146K.