If you have a good job that’s not too demanding and are still feeling this, then you might think about it as a health issue and look into it with your doctor. You have two paths:

1. look for some treatable malady - perhaps depression

2. focus on wellness and fitness: exercise more, get your electrolytes, fix your diet

Either of those two paths may lead to more energy. I don’t know how old you are but this kind of thing doesn’t get any easier with age so I highly recommend getting ahead of it as soon as you can.