Just out of curiosity, why would she not believe you? Have there been other instances where she didn't? If she doesn't believe you, that doesn't mean you have to hurt yourself to prove it. There are other alternatives. I told my mom I was depressed, she thought it was demons and wouldn't help me, so I went to a school counselor and she threatened to call social services on my mom. Hurting yourself is never the answer. What I would do is just tell her and don't let her not believe you. If you genuinely are suffering then do whatever it takes to get the help you need.