Hi ive been having left chest pains and shoulder and arm pains for 7 months been see gp and hospital had ecg everything seems fine im really worried?

Look for a: musculoskeletal or nerve cause for your pain. Pain in these areas is worrisome for coronary artery disease, you're right, but not in a 23 year old and not for 7 months. A normal ECG is also reassuring, as it can look into the past and show the physician if you've had trouble with your heart getting blood/ oxygen in the past. The cause is not your heart.