Given that you're 18, while I wouldn't want to rule out the possibility of pharmacological intervention, I would encourage you to explore some behavioral strategies first. There are professional therapists who could certainly assist you with this - they don't just work with those suffering from severe functional impairment; they can also help with mild to moderate cases of anxiety. Of course I understand that therapy may not be a feasible option at this stage.

From my own experience, I had a number of bad piano recitals early on in which my posture suddenly became rigid, almost as if I had regressed into the childhood logic of believing that no one would see me if I didn't move. In reality, I knew for a fact that all the other musicians in the audience knew exactly what they were seeing - a person playing badly due to nerves.

Fortunately I did find a cure for my problem. I started inviting people to my practice sessions, sometimes in exchange for some small favor or meal. These weren't my closest friends, who wouldn't have made me nervous, but people I knew from classes, lab partners, dorm neighbors, etc. I had them sit just a few feet away, and I would practice isolated passages - usually judging whatever the person had time for. I felt comfortable chatting - sometimes pointing out some detail about the composition, even though it was probably over their heads. But ultimately, that was why I was performing in the first place - to share a piece of music that I believed was worth sharing (and also to satisfy course requirements, but that was secondary).

This may not work for everyone but it worked for me. My practice sessions felt different enough for me to work through anxiety at a smaller scale. And in the performances I could think back to the practice sessions, with a curious but supportive person sitting by my side, not judging me but enjoying the process of discovering the mechanics of a piece of music that he or she had never noticed before. I also made some new friends and / or strengthened some friendships in the process. I'm still not a great public speaker, but one step at a time.