What Causes Lower Right Back Pain?
I understand your concern, however I would need you to fill in a little more information to help me understand better. Is that a constant pain, unrelated to body moves? Or do you only feel the pain when moving? What kind of pain is it? Dull? Sharp? Lingering? What is the intensity of pain? Please feel free to add any additional information you feel is relevant.
It sounds like a pulled muscle pain due to incorrect posture or an uncomfortable mattress. However, I cannot be sure unless you provide more details.