Vitamins/Supplements for Young Adults?

Hey ya'll!

So I have a question. And I'm sorry if it's already been answered but I didn't quite find it. (Perhaps didn't look hard enough. I apologize.)

Anyway...

I know it's important for everyone to take their vitamins but I mostly hear about the ones for children or adults 30+. What about for young adults like me? Specifically a 19yo female in this case. What should I look into taking as far as daily vitamins and things like that? What does my body need?

I know that each person is different and that Person A may need more of Vitamin "this" than Person B, while Person B needs more of Vitamin "that" than Person A. But overall, isn't there like a basic amount that I should be getting each day? How should I go about getting to it?

Any advice would be so helpful. I know I'm not getting the vitamins and such that I need and I've always had a weak immune system.

Also, what about for not only just general well-being but when you're working out and stuff. Like I hear about those protein shakes and stuff. Last year I'd take these little grape flavored Glutamine Chewies 30 minutes before I'd workout. I noticed a difference between the days I took them and the days I didn't. I felt better with them. Are they ok? Or is somethin' else better? Are different things required for different workouts or sports? I know these are a lot of questions. I'm just wanting to know what I should start looking into.

Thank ya'll!

~Meag