It doesn't strike me as tremendously weird for you to use foundation, but on the other hand, I wouldn't have really expected it either.
Irrelevant Skin Advice:
1) I doubt the foundation will be helping your skin overall, unless you borrow your sister's make-up remover to clean it all up. I know that when I start wearing foundation and too many things like that, my skin starts getting unhappy. MissHero's right about trying to prevent/cure spots, rather than trying to hide them.
2) Since your skin's not so good on your forehead, it made me think that if you have a fringe, perhaps that is irritating your skin, especially if it's a fringe that you're constantly flicking out of the way. Maybe a different haircut would improve your skin?
Sorry for throwing in random advice there - I know you weren't asking for stuff like that, but I thought it might be worth a mention.