You're normal, dear. I did the same thing until about my second year of high school. You're young, but you've already hit puberty (I suppose), and your body may be giving you sexual signals, and humping pillows is just your way of handling the sexual impulses. Which, I will say, is a lot better than going out and having sex at your age, which can have many bad consequences. This will pass as you get older, but if it does not, and it bothers you, you could consider getting counseling from your doctor or other health care professional.
