Well stress will definitely have a deleterious effect on your energy level. However, without much more detailed information I'd guess its a nutritional deficiency. Even if you don't think your diet have changed radically in recent, your body does often change the way it processes nutrients particularly as we age.
In any event, you can't diagnose this on your own. You really do need to talk about it with your doctor, and at minimal get a complete blood work screening.
Last edited by KraneXL; 10-06-18 at 11:44 PM.
Reason: clarify