Thanks for query,
Your daughter has irregular periods
due to hormonal
imbalance.Initially when periods starts due to pitutary glands precursors not regulated initially leads to irregular hormonal surge develop this situation.
you should keep her on birth control pill for atleast 3-4 months so that her pitutary learns how to release precursers of hormone.
& chest hurts is a complication & symptoms of anemia
so give her enough vitamins & iron .