My 11 year old daughter has pain in the upper chest , no pain in the arm, when you lift your right arm or lean , it affects breathing . Could it be stress from school?
It can be stress, it can also be a pulled muscle . It could be pleuritis, is an inflammation of the lining around the lungs and breathing or painful in some positions . If she does not have fever, cough test with ibuprofen , if it appears to be sick take her to the pediatrician.