I Can't Decide on 1 Position

Ok I'm 18 and in love with the girl of my dreams. She is so nice and a bad girl in bed. We were each other's first (as far as sex) but we have a problem during sex; I can't stay in 1 position long enough. I kinda get bored and like every 5 min. switch positions. She asked me yesterday why I do this and I said I do not know. She said that she almost has an orgasm and then I switch I don't know why but I can't stay in 1 position. Can you help me please?

Thanks yours truly Joey