An easy way to eliminate back pain while sitting is to restore proper sitting posture.
Observe the following instructions to sit properly in your chair:
Your head should be directly in line with your neck. Having your chin tucked in slightly. Keep the ears over the shoulders.
Both shoulders should be level.
The middle of your back should be straight.
The hips should be in line with the shoulders and the ankles should be in line with the hips.
When sitting the hips and knees should both be at 90 degree angles.
Maintain a natural curve in the low back (referred to as your lordosis).
Good luck,