You might want to get tested for anemia . . . I was tired a lot a few years ago and found out I was anemic when I went to donate blood and they turned me away because my blood iron was way too low! I am not vegetarian and took regular multivitamins, but I still get fatigued and sleepy if I don't take iron supplements. Just make sure you take the slow-release ones, my Dr told me that the "all at once" pills cause, er, bathroom troubles. So right now I take an iron-free multivitamin (I don't want to take unhealthily high levels of iron either) and then a separate supplement called SlowFE for anemia.
Especially during winter, make sure you are getting enough Vitamins C and D if you aren't eating citrus/leafy veggies and sitting in the sun!
