On and off upper back/chest pains for 48hrs. i do a lot of cardio in the gym and abuse laxatives but i'm trying to wean off. what could be wrong?

Musculoskeletal: It is difficult to say without examining but the pain you are describing sounds like musculoskeletal or nerve pain. The chest pain may be due to a strained muscle or referred pain from a pinched nerve as well or due to inflammation of cartilage. However you need to rule out involvement of your heart and lungs as well. You need to get examined by a doctor to get the correct diagnosis

It is likely that: you have pulled a muscle but with laxative abuse, metabolic derangements (hypokalemia) could be present that would also cause musculoskeletal discomforts. Probably best to see a health care professional for a thorough checkup and perhaps some counseling for your laxative abuse.

Thoracic dysfunction: Is exercise related back/chest pain that is common in young people. Can be improved by physiotherapy and/or adjustments to workout. May also be some sort of muscular problem. Also possibility of this being referred pain from a lung or abdominal problem (heart possible but less likely in a young person able to to gym work). Therefore needs examination as per the others. Urgently if breathless