What Causes Muscle Spasms And Stiffness In Abdomen, Back And Hip?

I am having muscle spasms or muscles that will not relax once contracted until I stretch the opposite direction. This can happen in my abdomen, back, side laterals when reaching to wipe after a bowl movement, or even when shifting in bed at night. It seems that my muscles contract and keep contracting until I can stretch the other way to get them to relax. it is painful and a strange sensation. What could be causing this? I am becoming more concerned.