When you feel like you don't know who you are

Have you ever been in a situation when you feel like you don't know who you are and what you want? It's not like the kind of feeling that you have when you try to decide something. It's more like there are two version of you and they keep contradict each other. They keep fighting against each other. It feels like you have two personalities. From time to time you keep switching between one personality to the other personality. Your attitude toward your self, other people and life are keep changing, depending on who you are at that moment. If you've been in that kind of situation and managed to deal with it successfully, you might be able to help me. =)