Is Alzheimer's hereditary?

My great-grandmother died of Alzheimer's (on my father's side if it makes a difference) but she was very old when she died. Sometimes I will go into a room and I know that I had to do something in that room but forgot what. Or I will constantly forget what people say after five minutes or so. I will grasp the main concept but I zone out in some of it. I know I'm only 14 but are these early signs of Alzheimer's? Is it hereditary?