@bao3niang Figure out a way to strengthen your core and back, focusing on stabilization. Pushups, reverse pushups, planks, all the planks, light weight many reps deep squats, holding weight above/below/ in front of you, but not resting on your shoulders.
You are specifically looking to get ride of scar tissue, not power or "strength", while also trying to get your body to reset a little. I am going to bet you have some underlying hip issues as well. Just a bunch.
Another thing that has helped my hip and lower back stuff is finding a pull-up bar and just hanging from it. It will loosen up your shoulders, but I also feel muscle and joints on my problem side stretching out. Look to the sky when if you do this.
Get more protein/fats/carbs in your diet. They way your ribs and hip bones show added with the way your stomach sucks in, I would think that the front side of your core is weaker than the back side of your core, which would also lead to the "slouching forward" look.
Biggest things I see, not certified in anything other than personal experience, is core weakness and hip/lower back mobility issues.
Edit: protein/fat/carbs within reason. You have to have protein to build muscle, you have to have fat to repair tissue, and you have to have carbs for bodily functions. Don't eat Chipotle twice a day. Just saying.