I agree with 65'r - it is likely that the fatigue is due to an imbalance of some sort (like potassium from lack of bananas as ONE possible example). It could also be reaction to a medication. But most of those types of problems would be identified by a few simple, cheap and easy blood tests... I would start there and then, if they show everything is normal to seek a consult with a cardiologist (and have copies of the blood tests to show him so that he doesn't have to needlessly repeat them).