Well I've got news for you: Nobody is actually on the mood to meditate all the time. In fact this happens with myself: the first time I try a new meditation I'm all exited but eventually this wears out and I just do it reluctantly. The secret is just to keep up at the point you do it reluctantly and just accept it and focus at the present moment. You're not gonna be motivated forever, you know. This is only a temporary thing that wears out very soon. You just need to program your meditations and do them regardless if you feel like doing them or not.
The reason motivation doesn't work and is temporary is because it's focused on the future. When you're doing power meditations, only one moment exists: the present moment. There's no future or past, otherwise you'll just miss the meditation. There's only the present meditation you're doing. So you can see why the motivation thing is useless, especially for meditation. Because you need to totally focus on the present moment. If you're doing the meditation and you feel happy because you're thinking of a benefit it'll bring in the future, you'll obviously miss the meditation and it'll be as if you're not doing it.