Firstly, you must check if you are losing blood because of some issue.

Some of the common issues are micro-bleeding in the intestine or stomach, which can show up us very dark stools. Some women have a very heavy menstrual flow leading to low haemoglobin. Even tumours can lead to low haemoglobin. Once you have fixed the blood loss issue, you can improve the haemoglobin by consuming jaggery, black channa ( roasted/boiled), green leafy vegetables, raisins, beetroot salad, anar ( pomegranate).

Also reduce the consumption of tea, coffee and too many antacids tablets.