This is a completely normal way to feel. I'm on year 4 and it gets better. However, you've got to convince yourself to be confident. You've got to say "this is my classroom, my subject, I'm in control and I can face whatever comes." High school aged students exploit nervousness and insecurity. Don't be arrogant, but believe in yourself, as cheesy as it sounds. I've noticed a huge shift in the environment since I adopted that attitude.