A close friend was low most of the day and was not as lethargic or tired as you describe.

"No motivation" makes me wonder if the problem is related to the adrenal medulla, not adrenal cortex.

The former makes adrenaline-like chemicals for motivation. Look up norepinephrine.

Do you also have symptoms of "inattentive ADD?"

They can be related. Look up "catecholamines"

Are your hands typically cold, colder than most people? If so you might try selenium, or a supplement such as Thyroid Helper. That warms my hands and gives me more motivation. My butt becomes unglued from the sofa in the evenings.

You might also want to get a good thyroid panel, not just TSH.

You could also do temp testing.
http://www.drrind.com/therapies/metabolic-temperature-graph

With Cat issues you'll have motivation to do things you like and respond to emergencies okay but not have motivation for boring situations unless you are late in finishing them.

There are many things that could be involved with fatigue but with lethargy plus normal adrenal cortex hormones I'd consider Cats.