I have a tightness/pain in the upper left side of my chest this has lasted about 6weeks now and has become very frighting. it is most painful in the early morning or late at night or after a strenuous activity.

This : This sounds like angina. Angina is characterized by chest pain or chest discomfort that occurs when an area of your heart muscle is not getting enough oxygen. This is a dangerous situation because it can be a sign of an impending heart attack. You need to see your doctor right away for a chest pain work up. This will include a detailed history, physical, and necessary testing (including an ekg). From there, your doctor can decide on the next step. Typically this would be a stress test to evaluate your heart while it is under stress (usually exercise). This test can provide more information concerning possible blocked blood vesssels in your heart. Please see your doctor right away to begin the above process. Good luck.