I HONESTLY don't understand what I'm doing wrong ...?

I'm extremely frustrated and I seriously don't know what to do anymore! I'm taking a Biology cl which I absolutely love. And for SOME reason I can't do well on the tests. We had our midterm 2 weeks ago and I got a 72% and the rest of the tests i take i fail. Can somebody PLEASE help me understand what im doing wrong? sorry if i sound mean and all .... its just that im very angry and frustrated :(