I am looking for a book that explains General Relativity and the math behind it. I have read about the principles and concepts, but that just does not satisfy my thirst for an understanding of the theory. I'm looking for something that explains the concepts as well as the math and the derivation of the formulas (I want to know why the formula is the way it is and how the mathematician came up with it). I am a high school student (Senior currently taking AB Calculus) but I am not afraid of advanced math. I understand that I am not currently at the math level that I need to be at to fully grasp the theory but I want more then just a set of formulas with explanations of the concepts; I want to see the math behind it, at least as much of it as I can understand. Any book recommendations? Thanks.