Phase one has a tendancy to make people feel very run down and tired lore. It's because carbs are supposed to be your main source of energy, and although you are still getting carbs from veggies, it's not nearly as much as your body is used to. It will go away once you start to introduce grains and fruits in phase two.
Until then, i have no idea what helps. I find drinking alot of water and excercising makes me feel more energetic.
Best of luck!