Why do I have Schizophrenia?

I was diagnosed with schizophrenia when I was 14, im 15 now,I have been sexually abused when i was a child, but thats not the reason is it? I have bad and good hallutionations. I have a deep depression too, and I dont know why. Please tall me why! I have this voice in my head that hates everyone I love and tells me too kill them.