I'm Not Sure What Is Wrong With My Friend. He

I'm not sure what is wrong with my friend. He is 17 and male he told me he has been having difficulty breathing, chest pains, fatigue, lightheadedness, he once passed out due to these things. We have been trying to find something but come up short continuously. Its not asthma because he has been checked for it. Although he has had a large number of concussions im not sure if it is playing a part in all of this. I would just like to know what he may have. Thank you.