I'm really suprised at that, 2 stone is a very substantial amount to lose, i would of said you would have dropped at least 2 sizes, i have dropped one and i've only lost 9.5lbs.
Have you had children? This can change your shape completely, your hips may be wider now and you may always be a certain size around the hips.
Do you exercise? It could just be that your muscles need toning up a bit, that way they will shrink tighter and you are sure to drop sizes.
Good luck xxx