Thoracic kyphosis in a young person is quite often caused by Scheuermann’s changes within the discs and endplates themselves. It results in a congenitally or rather developmentally increased kyphosis, even to the point of anterior wedging of the vertebral bodies. This is NOT typically associated with trauma (although trauma can result in an exacerbation of the problem) but is caused by a congenital (genetic) predisposition.
The current thought on its occurrence is that there is vertebral body endplate vascular inadequacy (once again typically genetic) which then results in inadequate vascular supply to the adjacent disc. This results in early breakdown of the disc and hence the adjacent vertebral endplates causing a ‘wedging’ and thus kyphosis.
Scheurmann’s kyphosis typically occurs in the mid thoracic spine and can extend well into the lumbar spine. Given an exaggerated kyphosis in the thoracic spine, the body attempts to ‘realign’ in a compensated manner, putting the body weight directly over the center of the hips, which requires an exaggerated lumbar lordosis.
Given that your symptoms began as a teen, I would venture to guess that this might be the case for you. Midback pain in teens is quite common, and I can almost guess what I will find before I ever image a patient of this age, depending upon his/her history and symptoms.
Unfortunately, there is no known cure and no amount of supplementation, physical therapy, etc has been shown to improve the overall alignment although during the ‘growth’ phase, it can diminish progression. Certainly, strengthening the core musculature will allow people with Scheuermann’s to be more stable. However, there is no way to realign, because the actual BONES and DISCS have changed, and their baseline support is the main vertical support of the body. However, this is also typically self-limiting, and the kyphosis and lordosis will usually stabilize after the final skeletal growth phase.
It might be worthwhile for you to see a spine physician. A simple lateral X-ray might be able to rule this problem out. At least knowing if this is the cause would allow you to work on your body understanding its limitations.
Here is a link which is basic, but gives a bit more information. I trust this site and use eMedicine.com often.
Scheuermann Disease: Practice Essentials, Pathophysiology, Epidemiology
This is another good link with a very good explanation
There are alot of trash links on Google… especially one self serving YouTube video. As always, be careful with all medical advice/explanations given on the net.