I have scoliosis and a chronically screwed up upper back. If I sit at a desk with a bad ergo setup, I will experience back pain within 30-45 minutes. I'm pretty tall, so the majority of desk setups are, by default, too short, and force me to hunch over my keyboard. A good chair helps as well.

Besides that, regular exercise helps tremendously. Seriously, if you do not exercise at least twice a week, I would strongly advise making beginning to do so your highest priority.