Vitamins don't provide energy. Calories do. If your'e tired, you have to consume calories. Vitamins won't help in that regard. Unless the vitamin has sugar- then you're getting a boost and energy from the sugar/carbs.
Calories are your body's ONLY source of energy. Carbs, Protein, Fat, Alcohol. One of the biggest nutrition myths is that Vitamins, (usually associated with C, and herbal recipes like ginseng) provide energy. No vitamin produces energy. B vitamins help release energy from calories though (they are not a source of energy themselves).
So if you're tired, eat but eat light. Even a glass of cold milk should be enough for a little while.