Is this normal? Why did I behave this way as a child?

If I had to describe my childhood, I would use the word unusual. Even before I knew what sex was, I would often think about it and masturbate. I began behaving sexually when I was 4, which is when I started remembering things. I have no memories before then. I'll explain why that's important in a minute.
First off, I'd like to say my idea of "pleasure" at the time was twisted. I touched myself in a way that would HURT instead of feel good. I'd rip out my hair, put it in my vagina, and slowly pull it out. I don't know why. My thoughts were just as strange. I would play with my toys inappropriately. I'd pretend one doll was raping the other. As I got older, I entered a phase where I was fixated on rape. At the age of 12, I could not fall asleep until I've imagined someone holding me down and hurting me. Though, maybe that was from guilt.
When I was 6 or 7, something happened to my older sister. I woke up to her screaming, then my next memory is of us being at the doctor's. They examined us both. I found out 7 years later that my father had raped her for 3 years. Only my sister knows the full story, but I can't ask her about it. She doesn't want to talk about it.
Now, as far as memories go... They're really hazy. I don't remember much unless I look at pictures or visit a certain place. I don't know how my father could have snuck out of bed every night, because I was right there. I used to sleep beside him. The idea of him being a rapist seems impossible. I just can't wrap my head around what happened, or why I was so obsessed with rape afterwards.
I don't ever recall him hurting me, and I don't think I saw him hurt her. I remained innocent, but my mind was out of my control. How could I have had such terrible thoughts, when I was never the victim? It doesn't make any sense.
I need some closure to this, but I can never get it... My father hates me, and my sister is too traumatized to think about it.
Is this normal? Why did I behave this way as a child?
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