I have a serious problem with my sister?

You need a mature adult male figure to talk to. Females tend to stick together. Unfortunately, your sister may be 20, but she certainly doesn't act like an adult. At her age she should be more understanding toward you. What, she can't remember when she was 15? Try to avoid any situations that seem to "set her off". If she starts yelling at you again, agree with her. Tell her she is absolutely right. Back away from her, continue to agree with her (what, she's going to tell Mum that you were agreeable today and should be punished? If she calls you names, quietly say, "you know, I have been a (fill in the name) I am really sorry. Back away. Pretty soon she is going to realize that you simply are not going to argue with her, and she will leave you alone. Please try to find a male adult you can talk to, one who is trustworthy, who can give you guidance. Hope this helps. Life can be unfair sometimes, and we learn to deal with it. When it is unfair all the time, that is when help is needed.