Sounds so familiar. Last year, I was working too much and when I was home in the evening, I couldn't even watch the tv. I'd suggest to pay a little more attention to your needs - take a five minute break every hour or two, drink a cup of green tea or whatever makes you happy. If you have a nice view from your office window, enjoy it, if not just go out to drink your cup of tea - away from work. Take your camera on weekend and go take pictures of spring flowers or birds.

And check if the lack of vitamins it's not the cause.

Well, that's what helped me.