Already flat straight out I can tell you you dont have DID(Multiple personality disorder). What your talking about sounds like Borderline personality a little bit, but i wouldent say you are. From what it sounds like, your'e just trying to learn yourself. Multiple personality is when your whole personality changes and later when you switch back to the normal you, you forget what happened. Unless your going through something alike this, i dont think you have to worry. Lol and im quiet, loud, shy, and outgoing all put together. So it's hard for me to understand myself, but it's just me.
PS: There is a girl at my school with the disorder.. Her second personality is "somone that speaks in car languge." At one moment she might like you and be nice, the next shell be saying "meep meep" and being rude. It's a little funny but pretty sad.