I had slight left chest discomfort and it is now with armpit region. i had my x-ray , ecg, echo and ct chest scan and all are fine. what it could be ?

Chest pain: It certainly sounds like you have a pretty good evaluation of chest pain. It's important to know whether or not this is related to exertion or occurs at rest. Given your age and certainly if you have no other medical problems including hypertension, diabetes or elevated cholesterol it would seem unlikely that this is related to your heart, however perhaps a stress test evaluation is in order.