What Causes Pain In Back While Leaning Shoulders?

Age 28, male. Back pain located in the middle of the spine. Pain is mostly felt only when i bend over by bringing my shoulders forward or when i lean back by bringing my shoulders back. Usually pain is never felt when laying, sitting, walking. Sometimes felt when getting up or sitting down, also sometimes when turning. Pain is located in one spot, does not spread in any direction. I think this may have been caused by me carrying my school back-pack which always had my laptop in it + other school stuff.