I have been through this situation a lot. Since childhood they wouldn't believe me. The best way to avid this self doubt is by acknowledging the fact that you know you are saying the truth. When highly don't believe you just don't talk to them about things you want their attention. I had done this and 2 weeks went ok until the school management called my parents. When they asked why I didn't tell them sooner about being bullied I just said cus you never believed me.When you know what you are going through you can get through it yourself. When they do not believe you be consistent on you words. And you are the only one that need to acknowledge your efforts.