Hello and welcome to Healthcare Magic. Thanks for your query.
You have mentioned two things here - about hearing voices and about your 'other personality' called Mandy. These symptoms are likely to be due to a psychotic illness. If you are hearing "mental voices" or having imaginary mental conversations or feel that you have an "alter" personality, then this could be indicative of a dissociative identity disorder (commonly known as multiple personality disorder
A detailed history and a proper psychological assessment is necessary to ascertain the correct diagnosis. So, I would advise you to see a psychiatrist
for a detailed evaluation and further treatment.
Wish you all the best.
Dr. Jonas Sundarakumar