Hi
At the bottom left of iTunes there should be 4 square buttons. They should all be grey. If you have the 3rd button in blue with a little 1 next to it, it will repeat one song. To change it back to normal just keep on clicking the button until it's grey again.
I hope this isn't too confusing for you.
EDIT
lol sorry, you mean on your iphone, not itunes lol.