First off, I think you need to give yourself a day off during the week. Sometimes just having a day off to look forward to gives me the motivation to just get myself moving for that day. Make sure you're doing a variety of workouts, too. Boredom really plays a heavy part in quitting.
And sometimes it's just a matter of ignoring that voice in your head that says, "I don't wanna work-out today." And tell yourself that you really do. It's the same principle as giving in to something you don't want to do because you're telling yourself you're NOT going to do it, instead of telling yourself you're going to do the opposite. You know, if you keep saying, "I'm not going to cry. I'm not going to cry." And all of a sudden....you're crying. If you say, "I'm under control. I'm under control." You will be under control.
"I want to work-out. I want to work-out. I LOVE EXERCISE!!!!"
It works. I swear.