Hi little brother. I'm 27, a doctor, specialising currently. I know what you're going through. Firstly I want you to know that you aren't alone. It's tough to be laughed at, but it's more important to respond rather than react. Respond with a smile even though it makes wanna hit them. Be positive. Next, seek help through speech therapists and the like. Channel your frustrations into something positive(education/sports or whatever you like) How people react doesn't define you. Don't hope for a quick cure, there isn't any. You can get better through practice and patience. Good luck kiddo. I'm rooting for you!