Wow, that sounds kinda miserable. Your love for art must be immense!

I lay down when I draw. Mainly because I rarely get the chance to do otherwise. But maybe that will help?

I used to draw in that position, too, and it does hurt. D: It takes a little bit of getting used to, but try resting the edge of the clip board/sketchbook on your collar bone/shoulder (a bit like a violinist). I also recommend getting a desk lamp that you can adjust and a good light bulb (I use a natural light florescent bulb in a portable lamp with a clip on it so I can attach it to a table; it sits just over my left shoulder so most of the light is right on my paper). I also recommend getting a good hard-backed chair. You'll want a cushion to sit on, but the back should be hard wood and straight so you have something to lean your back against.

I've had scoliosis all my life, too, and it's tough to work with sometimes, but if you make some adjustments you can cut down on your pain a lot. I'll see if I can get some pictures of my drawing set-up if that will help. :)