>but that just seemed to make me more tired.
>I'd be a pretty poor parent if I came home with this level of energy every day.
This isn't energy, it's depression. Even if you are not talking about "burn out", talking about your energy levels is a mood issue, unless you are overweight, have a bad diet, or have irregular sleep (which, as you say, you do not).
I would mention these concerns to your doctor. 10% of US adults (http://www.healthline.com/health/depression/statistics) suffer from depression, and it has nothing to do with whether you enjoy your job. The difference, if treated, is that you will enjoy your job and have energy at the end of the day.