The best way to have your posture assessed is to consult with your Chiropractor, Physiotherapist, or Osteopath. They will assess your posture in different positions such as sitting, standing, walking, or sleeping to have a better idea that which structures are at fault. Then they might prescribe specific braces such as a posture corrector as well as exercises to overcome the problems.
Also, you can test your posture without any professional equipment with the help of a family member or a friend.
The wall test:
You only need a ruler or tape measure and a helping hand.
First, stand against the wall, with the back of your head touching the wall. Place heels 6 inches out from the wall.
Your buttocks and both shoulder blades should be touching the wall. Have someone measure the space between your neck and the wall. Also, measure the distance between the wall and the small of your back.
Both these measurements should be less than 2 inches. If the measurement is greater than 2 inches, you likely have poor posture and a curved spine.