I have definitely felt the same way. For me I think it is the lack of mandatory routine on the weekends that the work week provides. The best the thing I have found for me is to keep as much of the morning the same as I can and do one productive thing as early as possible. Then I don't feel like I completely "wasted" a day.

The next best thing you can do is give yourself a break. Realize that you did your best during the week, and not being perfect everyday is fine, maybe even better for other parts of your life.