I have a lower pack pain, it feels like a stabbing/pinching feeling and only hurts when im sitting or standing but not laying down. what could it be?

Get checked: You need t to get checked . It may be sciatic nerve compression or piriformis muscle syndrome.

Disc dysfunction: The most frequent cause of precisely these symptoms with or without leg pain is a damaged intervertebral disc. The disc can be cracked (fissured), bulging, extruded or unstable leading to misalignment of the vertebrae above and below it. Mri is the best diagnostic test but x-rays (preferably performed erect) combined with laterals in flexion and extension can be very useful at times.