What Causes Pain And Stiffness In Back Muscles?

i ve had this low back pain for some weeks. i ve been trying to find the cause. i m very stiff in the morn n feel better as the day progresses. tonite i skipped for a short while using a skipping rope and i felt the pain more acutely. do u think the skipping rope is the prob? what muscles or ligaments etc do u think i am hurting?