joegrane
look up "catecholamine depression" and inattentive ADD. They can be related. It has almost nothing to do with feeling sad or "depressed" according to the popular understanding of the word.
I'm not suggesting that you have it, just that you'll want to rule it out. It involves feeling unmotivated and lethargic except when something interesting is happing. You might feel glued to your chair when life is not interesting.
You could check out selenium. It can be good for a variety of situations and is a rather safe and inexpensive place to start.
http://www.wellnessresources.com/health/articles/seleniums_vital_role_in_thyroid_hormone_function/%20tionist
http://www.healthline.com/health/selenium-an-essential-mineral#1
Eventually you'll want to check your iron levels.
Some people find methylation support--multi B containing B12, folic acid, etc to be energizing.
This won't apply to most people but I had a heavy metal problem. HMs affect so many systems in the body, a number of which contribute to fatigue when not working properly.
CoQ10 and carnitine are two to consider for mitochondria support.
My previously good health went South around your age. I did not even start to get improvement until a friend convinced me to stop treating my mainstream doctor like a benevolent medical god.
Even some doctors had a long list of mysterious symptoms and had a tough time figuring out what was going on. Dr Mark Hyman and Dr Jerry Tennant were two doctors who were essentially disabled by their mysterious med problems. The solutions for them were very different, but in both cases their mainstream doctors did not have any solutions.
tennant
https://www.youtube.com/watch?v=6XicmDDmVBs
hyman
http://www.youtube.com/watch?v=wkxk7nod33o
Don't forget to check out GABA, glutamine and magnesium for anxiety.
Good luck as you try to chip away at your medical problems.