I have the same problem and I've tried different things and here is what I've come up with
1.Diet - if you don't eat right then you won't have any energy. I've found that eating a lot of fresh salad with only olive oil and vinegar on it is good for cleaning out the digestive system. Other things is to eat less carbs. You don't have to go all out on the atkins, but eat meat, green leafy veggies, and some other veggies. Avoid rice, potatoes, corn and other veggies that are mostly carbs and sugar. Eat fruit starting with the letter P. My wife went to a doctor and that is what she was told is good for digestion. Don't drink soda and other high carb drinks.
2. get some exercise
3. vitamins - find good natural vitamins that don't have artificial ingridients like some crap that is sold in supermarkets and drug stores