Exposure was the only way out for me. Presenting scared the hell out of me but in high school forced myself to take a presentation class where every student had to give a speech a few times a week. It was rough. Really rough. I think I've blocked out most of that time from my memory because of how embarrassing it was. But it helped me a lot mentally. Eventually you'll get used to the pressure, the racing heartbeat, the feeling of a block coming up, etc. And over time you will start learning how to handle it, and your fluency will slowly start improving. It really helped that my classmates were supportive and kind. Don't give up.