Try pushing against the sheet that you are leaning on with your heel, feeling as if you are unfolding your body. Instead of bending and straightening your waist, you are unfolding your body by pushing with your legs.

Lower your waist just a little, like a little wiggle.

You should not hang the barbell on your waist; it should be lowered to your hips to stimulate your glutes. Also, keep your chin against your chest, and your chin and chest should rise and fall together. If you only move your waist, it can cause strain and pain.

I'm also similar.. They say it's hard to do.