Thank you for asking this question.
You told you have habit of eating chalk,this is a medical illness called 'PICA" and you are suffering from this type of abnormal appetite.This is due to inborn deficiency
of iron ,calcium ,zinc and other essential mineral in the body.
You must get your CBC and Blood picture done.Also take a course of Deworming by taking albendazol. Followed by this you take Iron and zinc supplements.Take fruits and green vegetables.
And go for balanced diet.
With these steps you are going to improve.
Ok take care. All the best.