Hello, thanks for using HCM. It is not uncommon to find young girls with low hemoglobin levels. Anemia is caused by a hand full of various causes ranging from habits to pathological conditions. However, only an appropriate diagnosis of the underlying cause of anemia will permit an effective treatment to take up the hemoglobin desired within the shortest time possible. 11.3 is slightly low but not that bad and so you need to be rest assured rather than worrying and by so doing allowing your normal physiology to carry on. Common causes of anemia in young girls include: excessive bleeding during menses, poor eating habits and consumption of substances that chelates iron in the digestive tract etc. Once the cause of the anemia is known and classified either as iron deficiency or vit b12 or folic acid or hemorrhagic anemia, an effective treatment is instituted and there after, an improvement in the hemoglobin is expected. Red blood cell production typically last an average of 5 to 7 days. therefore in order to have a significant increase in your hemoglobin , you will require a couple of weeks (at least 2 weeks to 1month) while on the right treatment. Best regards and hope this helps.