Not knowing your diet or exercise routine, either of these could be causes of your lack of energy. I know when I started eating healthier, whole foods, and cut out much of the processed foods, I started noticing how much happier, healthier and more energized I felt. I still get tired, but not like I used to. I worked out after work, when I couldn't fit it in before. I've been working out before work the last few days, and I have been loving the extra time in the evenings. But take baby steps and make those changes!