I've felt less motivated the past 2 weeks or so. I understand your pain. The hard part for me is a lot more sports happen when it gets nice and I love getting a chance to get out and run and compete. I currently have 2 days budgeted just for basketball (my "off" days lol), but there are times when work is winding down and I don't want to go to the gym.
That said, don't be afraid to give yourself a day here and there. Do what you enjoy. As long as you don't stop working out all together you'll be fine anyway. Plus, it always leaves me WANTING to go back and lift after missing that day -- good way for me to get my motivation back.