Josine,
First, you need to tell your parents. What happened is not OK. It is rape. You did nothing to cause it - the incident in the bathroom does not give him the right to do anything sexual to you. It is not your fault. It is your brother who did the wrong thing.
If your parents do not take the situation seriously - then you need to talk to someone else - someone your parents will listen to and respect ----a teacher, a grandparent, a religious leader, an aunt - keep telling people until someone believes you and takes this seriously.
Tell your brother he cannot have sex with you again. And if he tries it tell him you are going to yell and scream and fight him ( and then do that!)
Do not spend time alone with your brother. If he is helping you with homework - do it in a room where your parents are.
Get a lock for you bedroom door. You can get a lock that is the kind that is used on hotel room doors - so you put it on and take it off when you want to. Don't let your brother know where you keep the lock.
You can use this same lock in the bathroom if there is no lock there.
It might be really a big pain - but you need to start closing and locking the door while you are in the bathroom. This isn't fair - but you need to prevent your brother from "thinking" he has a reason to rape you again.
What your brother did to you is called forced fellatio. When two people do it because they want to it can be a wonderful thing to do. Some people call this BJ, Blow jobs, oral sex, going down, and other things. Brothers and sisters do not do this together - when they do it is called incest. It is not only not a healthy thing for you to do because it makes you feel weird, but because it is against the law.
Talk to your parents, and if they don't take you seriously you must talk to someone else ------ keep talking to someone until someone listens. This cannot happen again. Please keep in touch and let me know what happens. I will be worried about you.
Susan