Hi there...
Wanted to share a link that gives a lot of good information about SD..
http://www.spine-health.com/conditions/spinal-deformities/diagnosis-and-treatment-scheuermanns-disease
If I may ask a few questions....
What are the Drs. saying about your spine growth? At 17....should be close to the end of that period.
Have they been having you wear a brace for the last few years off/on? I'm just shocked that your first back Dr....(What kind of Dr. was it?) Didn't see the changes as no one goes from the regular percentages of 20%-50% to 85% overnight!
And even though I know the surgery sounds scary....It really can be the best answer for someone with the degree of curvature that you have. Otherwise, I can't imagine with you describing that it is "crushing" your lungs..that you are able to do much of anything now like work, play, drive, go out with friends, get ready for college, etc.....
It just seems so awful that you weren't able to with your parents, find a Dr. all these years leading up to this to help you not get to 85%....
And if you can't do all the conservative things to help, then surgery is really the only option. As you will read in the link I gave you, because the fusion is in the thoracic part of your spine, it won't usually effect the motion of your back and cause further problems or pain down the road.
So, I would do as others suggested and work with your parents on finding the most skilled Orthopedic surgeon who has done many of these surgeries and make the jump now because being young, you have a great chance at recovery, healing, and getting on with the rest of your life in a much better place!
Hopefully they will also be ok with helping you with your pain until surgery can be done as well....
Keep us posted..