@mamaherrera video tape yourself doing the movement. I would put money on guessing that your pelvis is rocking forward (anterior pelvic tilt) (google it for reference) causing your low back to be in a shortened flexed position which in turn lengthens your ham strings and makes your low back so tight/irritated that finding your glutes/hams is near impossible.
Basically you need to shift your pelvis to a posterior tilt on the way down in the movement with your knee of the foot on the floor bent for hamstring glute contraction and maintain that position all the way to the top and then reset that before the next rep. Two other cues would be Make sure that your stomach has a concave vacuum effect from the top to the bottom all the way back to the top. Picture an old man showing off for a younger lady at the beach when they suck their stomachs in.
Also make sure that the knee of the foot on the floor stays bowed out beyond the foot and hips slightly to ensure that your glute is turned on throughout the entire movement. Don't exaggerate this to the point to where your knee is out of alignment with your foot and your hip but just make sure that it's rotated outward a little bit. Otherwise you will definitely lose your balance and lose the entire point of the exercise because you will have the wrong muscles contracted. Hope this helps.