Please do improve your diet as much as you can! It will really speed things along. :)
At the outset of things, cleansing is more important than vitamins. Until things are cleaned up, you won't absorb them properly anyway. A good multi-vit/min that I like is Solaray's Spectro. You can only get it at good health food stores, not drugstores. It recommends taking 5 pills a day, but you can just take 1-3 really, like one with each meal. I'm not a real big fan of megadosing vitamings except in some cases. :)
There's a lot to learn and best to start now! :) I have Acne notes in my FAQ feel free to peruse all the notes, they'll make you smarter than the average DOCTOR about healing naturally. ;)