But it sounds like she told you she was unsure how she felt before you made the conscious decision to keep hooking up with the hope that she would come around, then after a couple of weeks you got annoyed that she hadn't made up her mind yet.

If her changing her mind was so important to you, then you could have easily cut ties with her before those two weeks. Her stance didn't change over the course of those two weeks, just how you interpreted it. She was okay with how things were. You weren't. Obviously she wouldn't change anything. If you wanted something different/more, then you needed to be the one to stop things.

It seems like the only thing you can't understand is that a girl can like you, but not be sure how serious she's willing to get with you. She's still a teenager, it's perfectly normal to still be figuring shit out in life. She wants to keep things casual. You want something more serious. Either casual is good enough for you or it's not. It doesn't mean she doesn't like you or doesn't care about you.