Is There A Better Sex Position For Our Situation?

I was having sex with this girl the other day–missionary position–and after a very short time she says it’s too painful. I admit that at this point I was very pleased because she’s obviously implying that I’m big.
Anyway, I suspected it would be better if we tried a different position, and she concurred. I asked her what her favorite position was and she said she didn’t have a favorite. So I went on to doggy style, and was very gentle. However, after a very short time, she said that it was still too painful and we, again, would need a new position.
So I let her get on top thinking she could have control and, therefore, pain could not be an issue. The same thing happened; this time we couldn’t even get started before she was in too much pain.
We decided we’d try one more position, and if it still didn’t work, we would just try again another night. I told her to choose the position, and she said she’d rather I chose.
I said, “I chose the last three, and none of them worked, maybe you’ll be luckier with picking the next one.” She said she didn’t know any positions. Amazed that someone doesn’t know any positions, I asked her how that’s possible.
She said, “Well, what do you expect, I’m only twelve.”