Why do people hate me? I am not a horrible person, I'm actually really nice?

I have always had problems at school with people. People seem to dislike me, I have never done anything wrong to hurt theses people and it's really getting me down. I am a friendly, moderately shy girl and i'm quite pretty ( I never flaunt it around though). I feel like i'm stuck in the middle of everyone, I have never belonged to a circle of friends and I just feel really lonely. My friends seem to come and go, I have just left compulsory education and I am planning on going back to school to do my A levels but I don't want to be lonely again, Is there anything I can do to show people the real me?