Vitamin B?

Hey guys, I saw somebody post about a Vitamin B (B-6? B 12?) that they took and it made them energized, etc. Anybody know which one is best?

(I’ve been feeling a little low, even though I’ve been sleeping plenty and eating well and exercising enough. I feel like I’m not getting enough nutrients, so I’m thinking of taking a Vitamin D supplement, because it’s not sunny enough here and maybe Vitamin C to make sure I’m not getting sick …).

Also, would it be better to take all the vitamins separately or to take 1 Centrum that supposedly has all the vitamins you need?

Thanks guys!