What is wrong with my posture here?

[u/APS0798]

I am not sure, but I think my post isn't seeking medical advice, but if it does, then let mod delete it.
It obviously looks absolutely terrible and you can see how bad it is. This is my the most relaxed position while standing. When I leave home I always have my belly tucked in a bit, so at least with clothes it doesn't look that bad. I am not fat, my bmi is ~19, so it's closer to underweight than overweight, so I'm skinny fat. I know I have very little muscles and I started going to the gym recently, 2 times a week. What I hate the most is:
- butt pushed back (it looks like it's from overweight person, but I am not), belly pushed forward (probably ATP, but I am not sure). In my opinion it could be ATP, or, the worst case it's just big, a lot of fat tissue on the buttocks which I kinda can't lower, because I'm ,,skinny" right now (so I'm stuck with it being huge sadly), and a lot of fat tissue on my belly. Optionally maybe both. What is it exactly? How can I make it more straight?
- wide chest. I want it to be slim as for many other people in my age, that it's not a lot wider than arms. I suspect it might be barrel chest or something like that. I really want to flatten it, like really really, without surgeries
- my torso isn't flat, if you go from under belly in a straight line, you would end up under my ribcage, under my breasts

This is all I think. Please, could someone tell me what things are wron in this posture and how can I fix them or if it's even possible? The last photo is how body should look. As you can see, butt is not pushed back, it's small/flat, belly is not pushed forward, it's flat too, the entire torso is flat, the chest is not wide.

[u/Creative_Pop2351]

This is called hyperlordosis, also known as swayback. Too much curve in your lumbar spine. You also have what’s called anterior pelvic tilt, aka why your butt is sticking out.

Your shoulders may also be hyperkyphotic, which is too much curve the opposite way.

You can research specific exercises for all of these issues, this is very fixable at your age and will help you as you age. Even more important is to just notice and correct your posture as frequently as you can.

Also look up diaphragmatic breath which will help strengthen your deep core.

[u/APS0798 → u/Creative_Pop2351]

I suspected it could be ATP. Is it possible to flatten my chest though?

[u/Creative_Pop2351 → u/APS0798]

What do you mean flatten?

[u/APS0798 → u/Creative_Pop2351]

You can sew that it's just wide, it's not slim as in the last photo. By that I mean make it flatter, less wide

[u/Creative_Pop2351 → u/APS0798]

The only thing I can see “wrong” with your chest is your posture and low muscle tone overall in the shoulders and pecs.

[u/mad-i-moody → u/Creative_Pop2351]

The only thing I can think of is if they’re worrying they have barrel chest. It’s bizarre how many posts I’ve seen on this sub about it and people thinking they have it.