What is wrong with me?

I do not know what is going on with me but this school year is not the best for me. For some strange reason, I am not doing as good as I want to on my school work. I am trying but it is not working. It seems like I know the information but when it is time to take a test on it, my mind goes blank. For example, I had a math test last week. Before the test, I was doing well on my homework and good on my quizzes. The last test I had was a reasonable score. It did not bring my overall average down much. After I took the first test, my average was a B. That is good and I was trying to maintain that B. After the test, I was still doing good on the homework and quizzes, even though I had a little trouble figuring out some of the problems. The information was in my brain. The night before, I looked over the chapters that the test were going to be on, making sure that I understood the problems and the solutions. I probably should have looked at the chapters that whole week. Finally, the test date came. I looked at the problems and my mind became dumb. I was struggling with some of the problems and the others were okay. I made a grade so low that it dropped my grade down to failure. I was thinking, "All that work I put in to maintain this B and this one test dropped it so low that I could fail this course." I am going to work twice as hard to pass. My mind went blank on my biology test, even though I studied for it. I did not even look at my test score that is posted up on the wall. My chemistry lab quizzes, I do the same thing. I could understand the material but when it is put in front of me, I look dumbfounded. It is the same way with all my other classes that require tests. I need to pray harder and study more. If that do not work, then I would not know what to do.