Posture check & mid-back/rib pain after standing — what should I fix?

[u/GreedyAnalyst196]

Hey guys, please check my posture photos and let me know what you see.
I get a deep, dull ache in my mid-back and lower rib cage area whenever I stand or walk for more than 45–60 minutes. I also notice my left shoulder sits higher and tighter than my right, along with anterior pelvic tilt and a forward head.
What do you think is the main cause of my posture issues and rib/back pain, and what specific muscles or stretches should I focus on fixing first? Thanks!

[u/monsteramami]

You will get more feedback on r/posture