Here is what I think it is.
All you movement comes from your low back. You don't move from your hips. One way you can tell is when you shrimp move. Does you butt move first or do you round your low back to start you the technique. If you round your low back you use your low back to move your hips. Another way, is to take your hand touch your low back. Find your spin, are the muscles next to your spin higher, like there is a valley with the spin the lowest?
If those muscles are higher then your spin you are using your low back to move or lift. You have weak gluts and you don't move or use your hips or gluts.
You need to work on getting your gluts stronger and learn to move from your hips. You can do a search on how to do glut or hip bridges. Dead bugs, birddogs. Also look up hardstyle plank, and hip flexor stretch. Stretching can help but until you change your movement patterns and strength your gluts it wouldn't be as Effectiveness as strenghting.