This used fo happen to me a little bit but the pain would go away more quickly than yours does. It hasn't happened in a while, and I think squeezing my abs harder throughout the whole set helped. Keep squeezing your glutes hard while you do this.
Do you wear a belt to bench? Also, I would guess that proper leg drive would help more than hurt something like this. A video shot from the side might be helpful to rule out anything silly.