I would look at your sleeping, dieting, and exercising habits as they are critical to your energy levels. There is a direct link between people suffering from fatigue and those factors. My mother suffers from fibromyalgia which has serious effects on energy levels. For years she blamed the fibromyalgia on being tired all the time. I convinced her to cut carbs and do some light exercising - low and behold she had more energy and felt better after weeks. Granted she doesn't run around like a teen but she gets fatigued less, her blood sugar levels are more regulated, and she has better sleep cycles. Same for my diabetic stepfather. Its really simple to see if you spend 1 week writing down when you wake up/go to bed, what/when/how much you eat/drink, and what your daily activities are. Even if you think you are living well, most people are surprised when they put it down and paper and have a someone else evaluate it only to see that most of what they do is contributive to low energy levels.