Who am I?

I've spent my entire life trying to be what you wanted, that even I don't know who I am. I can be the sweetest girl if you want me to be or I could be the meanest if that's what you'd prefer. If you'd like, I can be strong, but if it makes you happy, I could be weak instead. If you need me to be soft and feminine, I can do that. If you need me to be hard and masculine, that works too. But who am I when I'm all alone? to be honest, I'm not quite sure anymore. I'm so many things all at once, that I end up becoming nothing at the same time.