If exercising keeps you on track with your eating all day, then go ahead and exercise on Sundays. Since you enjoy walking, why don't you try one of Leslie Sansone's "Walking Away the Pounds" video workouts? They are a lot of fun, and you really get a good workout. You might be able to borrow one from the library to try first before deciding whether you want to buy any. And
to you for being so dedicated to working out!