Puberty irregular menstrual cycles

Hello,
My 14 years old daughter has irregular menstrual cycles on every two weeks, for over 2 years. She feels very weak, and her hemoglobin is very low. She constantly take Fe, but her hemoglobin cannot be increased. For 6 months she took a hormon therpay, but after that, her cycle became irregular, on every two weeks, again. What is your advice about her problem? Thank you in advance.