Off and on pain with movment & certian postures in rib cage,sides and back.it goes away when i stop movement or change posture. what could be reason?

Rib or thoracic d/o: Your symptoms could involve a rib fracture or a thoracic spinal problems. The latter could be facet pathology (the joints between vertebral bodies), thoracic disc pathology, or an impinged thoracic spinal nerve. It could also be a simple sprain of a costal muscle or a bruised rib. If the symptoms persists for more than a week, You need to see your PCP for a referral to orthopedics & imaging.