Hi, thank you for using health care magic. I can understand your concern. First of all, get your routine blood test particularly Hemoglobin. IF any of them is abnormal try help of doctor to correct it. Many times underlying stress or anxiety also reflect in this kind of habit. I would see your problem as habit or behavior which you would like to change. I understand you may have tried in quitting your habit. For increasing chances of quitting be aware of clues,thought, state of mind which lead to this behavior, try to change those precipitating event. Try chewing gum to reduce the craving for particular moment. Keep chalk piece and associated things away from sight this will reduce the craving for chalk piece. IF this not help you then consult psychiatrist , behavioral therapy and/or SSRI medicines will help you. Calcium tablets are readily available in market counsalt your Family doctor for best brand available near you.Few of them are shelcal,biocal,aiscal etc. Hope this will help you. Regards.