Concentration

Nothing is more annoying than trying your hardest to concentrate and you cannot at all. I'm not ADD or ADHD but I just dedicated myself to AP Psychology for over an hour and I couldn't do a thing. I hoping my brain will change things up and allow me to study in the morning before my test in fourth hour.
I'm saying a little prayer that this will work. I have an A- and I cannot afford to receive a B in this class!
HELP!