First of all there is nothing wrong with you other than teenage anxiety..but if it really gets worse, talk to the school psychologist.
Hey listen, Test usually get people nervous. Im pretty sure its normal. The most important thing you have to remember is, Study. As long as you've done that, you will pass. About the nervous thing, when your taking your exam try this. If you feel you cant concentrate, Stop yourself Take a really deep and long breath, Close your eyes and say to your self "I can do this". if u need to calm down further try tapping your pencil softly to a rhythm and go over the questions slowly till the answer pops into your head.
Good luck im sure you'll do fine
Most people experience stress and anxiety and have problems with it throughout their lifes.
It's normal in life. What's not normal is when IT controls your life and you feel helpless because of it. When this happens the correct thing is to seek help and find out for certain if what you are experiencing is anything to be concerned about.
Speak with your parents or guardians about what you are experiencing. I'm sure they will help you decide what a good course of action is. Be open and frank with them about everything you are thinking and how you fee and do the same with anyone you may see about it for help.
Good luck and let us know how you do.
Sometimes it is because you are distracted because there is so much other stuff going on inside your head.
It sounds like anxiety but you may want to see your doctor to get everything checked out.