Mind over body
If you don't have any diagnosable cause for fatigue, review your diet
, mental health, and physical activities.
Make a daily log for all these 3 parameters, you may find there is some thing you can do to improve how you feel over all. Cut down all the sugars in your diet, avoid soda and juices, drink plenty of water. Detox your body, for this you may have to consult a naturopath.