Hello Eva,
I'm sorry that you are going through this... Maybe the idea of doing something evil is something that you are so afraid to do that the very idea of it overpowers your mind. We will try our best to help you and to support you. sometimes, the best way of dealing with these obviously painful and overpowering thoughts is to seek counseling... Have you thought about that? It might help you to get a handle why these things are happening to you.
Feel free to write what you are feeling as much as you want. Sometimes writing things out helps also...