I've been dealing with a similar, over extension issue myself.
Like you, after awhile my scapula and then my hips felt "frozen," just kinda locked into a bad position.
Push up plus and scap pushups have been good to restore motion. I also like "band shoulder tractions" where you use flex bands to assist the stretch.
For hips and glutes I've been doing tons of clam shells, hip hikes, seated abductions with bands around the knees, and seated Psoas lifts/holds with a mini band around the knees. Anything to get my hips mobile, and my glutes working to get my pelvis underneath me. And to keep my spine neutral.
Like Trevor mentioned, weak hamstrings are part of the issue. I don't know if weak hams made me overextend, or if being in over extension made them weak, but my hamstrings were garbage. I've been doing hamstring curls of all kinds ( 1 leg, 2 leg, standing, laying, bands, ankle weights) to get "connected" to them better. Then inverse curls (a bodyweight calesthenic, like an easy Glute/Ham raise) to try and move better.
For other stuff, 1 arm farmer's walk and sidebends have helped me get the obliques going, to help with posture, and a neutral spine.
Lunges with a dumbbell held on one side are good too. The off set weight challenges hip stability while moving around.