Honestly having something to look forward to helps me push through times like that. A concert, a planned day of going out even by yourself... Something.

I feel you on the lack of energy thing. My job kicks my ass and leaves me little motivation to do anything after work or on my days off. One concept I have heard that helps me is "don't have a zero day". It's ok to take a rest or a day off, but if you accomplish one thing, you will feel better about taking time for yourself. I guess that's only if you're the kind of person that feels guilty about it.

If you spend a lot of time indoors, maybe you're vitamin D deficient. Vitamin D is good for overall well being and energy.

Sometimes I just have to push through. My wife has a desk job and when the weekend comes, she wants to be active. I just want to chill. We meet in the middle and I end up having a good day with her.