At first slight back pain and i thought it was because i slept on a couch but then got worse and hurt through my chest and couldn't breathe! why?

Have a fever? cough?: Pain when taking a breath is due to the movement of structures involved in respiration: ribs, intercostal muscles, pleura (lining of the lungs), pericardium(lining of the heart) and lungs. You may have simply stretched or injured a muscle of your chest wall, but if you have fever or a swollen leg, it could be more serious (like pneumonia or blood clot) in which case, evaluation would be indicated.