Hi Scottish_Player,
I agree that 23 yo is early for CAD, but it can happen. Note that CAD-related angina can also come on without any activity. But other signs of CAD or an impending heart attack are fatigue, a sense that you are dying ( hard to believe but see the "Merck Manual" ), shortness of breath.
My angina got so bad that I couldn't walk 50 metres at a very slow pace w/o it occuring. I finally saw a doctor. 99% blockage in one artery and 94+% in another. I knew before the testing ( angiogram, stress test, and echocardiogram ) that I had CAD, and long before the angina set in, I had a strong feeling that I was dying.
Well, I still think your doctor dismissed your angina or chest pain all too casually. Can your doctor tell you what it is that is causing the pain? I'd want to know what it _is_ more than what it _isn't_! I think I'd insist on a diagnosis.