Trouble breathing in when exercising

Patient: I AM A 17 YEAR OLD FEMALE. i have alot of trouble breathing in when i am exercising, particularly when i am running. i have been to a respiratory clinic and they conducted tests and told me it is not asthma but they were not sure what it could be. i can get air out fine but have trouble when breathing in. when this occurs i get headaches, chest pains and sometimes feel very dizzy and light headed. do you know what it may be?