I agree with the poster above me. Also, please remember that having to repeat a semester does not make you a failure as a person. Most people wouldn't attempt something so difficult as a nursing degree, so you're already ahead of those sitting on their butts! Many good nurses have had to take a semester over and/or repeat the nclex. Take this time to solidify your knowledge.
Also, could you look into getting a part-time job as a nursing assistant if you haven't already done so? I always have hard time picturing patients and their whole medical/nursing picture without getting some "hands on" experience. Maybe you could even do extra "clinical hours" by shadowing nurses? Whatever it takes to make the whole picture "click" in your head.
I recommend going to your instructors and using them as resources for study ideas and info. I'm sure they'll be willing to help you if you are eager to learn. Nursing school was really hard on me so I feel for you. Best wishes to you while you study!
I think you may find this book helpful:
Amazon.com: Saunders Comprehensive Review for the NCLEX-RN (R) Examination Full Color Reprint: Books: Linda Anne Silvestri
It's a really good general nursing outline. It's actually an nclex review book but they organize all the different nursing subjects into chapters and review them with basic nursing facts and nclex style questions....which is exactly what your teachers are probably doing with their tests! It's a great resource.