I had exactly the same problem as you at school. If there was a lesson where we had to do reading out loud in class, I would sit there with my hands sweating and my heart racing dreading my turn. It was horrendous. In the end, I used to skip classes where I knew there was any chance of me having to speak in front of people.
Beta blockers are very good at calming you down for something like a presentation. It's important that you sort out this problem because being able to speak in public will be very useful to you in later life, for example in job interviews. I just avoided it all together and never conquered my fear of it, but I really wish I had. Maybe talk to your teacher or something to see if they could help. Good luck.