It isn't unusual at all to feel so strongly about your grades. You know that your future rests on the grades and that makes them weigh very heavy on you. You need to try to relax a bit and then maybe your studies will sink in better. I think a tutor is a good idea but like I said, relax just a bit. You know what you have to do and you know you can do it. You should also know that it's okay to breathe a bit in between tests. It was only one test and you will improve the next time. I was once where you are so believe me I understand. Good Luck!