I'm watching my form in a mirror and on my phone and my back is straight, I'm squeezing my glutes, pulling my stomach in and still I only feel dead lifts in my low back mainly. If o lift more than 12 lbs my back hurts. I usually do 5 lbs or even no weights. I just can't figure out why I'm not feeling them in my glutes or hamstrings. Can anyone she'd light on this situation?