I really wouldnt term this "chronic fatigue" - rather than feeling drowsy.
Also, there is a natural "slump" in the mid afternoon for most people which creates these feelings of drowsiness or tiredness during the day. This is quite natural for people your age, and your activity level.
What you might try to do is take a nap, if you can, during the afternoon for about 45 minutes, but no longer, or you will enter deep sleep and feel groggy - you will also have difficulty falling asleep at night.
Also, try to get more natural sunlight if you can, - this has a direct effect on your melatonin levels, and how deep you sleep during the night!
Kacper M. Postawski, the Insomnia Terminator
End Your Insomnia and Enjoy Wonderful Sleep
without expensive drugs or greedy therapists