My 17 Year Old Daughter Can Not Have A Bowel

My 17 year old daughter can not have a bowel movement, she has not had one in weeks, she says she does not even get the urge to go. She can force a small one but she says it hurts and she has to strain hard. On top of that she has bad stomach pain, back pain, and it hurts to eat. Also, today she has had chest tightening. We have been giving her miralax with no luck. The pain is so bad that she can not even walk to the bathroom, so she doesn't even go to school. Any thoughts?