Hey Jonah. So you talked to your doctor about it? I had someone tell me one time when looking at me that I'd have a wrinkle on my face permanently if I kept squinting my eyes. I always squint my eyes so it never stopped. Guess what, I do have a wrinkle right there in the crease that is now permanent. So, there is validity to that.
I'm a recovered sloucher. lol. I had to start standing tall because I found I was getting picked on by rolling forward with shoulders and back. I guess it is a whole body language thing. My mom would always say 'stand tall and proud' and I was like "well, I'm not that proud". But as I got older, I got more confident and stronger mentally and I wanted to show it to people. I got myself out of the habit of slumping. It takes mindfulness. Being aware and consciously reminding myself to straighten my back, roll my shoulders back and lift my head. I also like to stretch and it helped get me up tall. Take a tall and put your arms behind you and pull the tall and it will open up your chest. Oh, speaking of this, I started to do some push ups and lift some weights and this all aided in my muscles supporting my posture.
good luck man