There are self inventories available...a list of statements or questions to ask yourself. I think it's always best to consult a therapist though. Are the voices EVER outside of your mind, or are they always "yours" in some way?

If you have some friends that say you are DID (multiple personality term was replaced by Dissociative Identity Disorder to better portray the process) .. why not ask them about what they see or think. Can they ask you for a name at those times? Perhaps you are DID. Would this upset you?

You can also try beginning a journal, with an open, written invitation for any other aspects of yourself to write and share. Sometimes that helps.

TC!