Try something like Animal Pak if you want to be sure to get everything you need. I wouldn't recommend taking multiples of your all-in-one, as it's real easy to get "too much" iron, etc. That is not a good thing!
im 13 and i take 3 centrum pills a day. my muscles have grown amazingly from them.
If this is true, and your not a troll, then listen to your dad and use your brain. Centrum isn't a particularly strong multivitamin, in fact, most of the ingredients are underdosed. However, it does contain 18 mg of iron, among the other metals. Iron is necessary in small doses, but in larger doses can kill you. The excess of the centrum isn't helping you build muscles, and the risk of toxic effect from the metals contained in the vitamin far outweigh any gain from multiple doses. Stop taking 3 centrum.