I recently took a week off from the gym, no exercise and sitting all day, I was in lower back pain bad. Every time I get up my right side was stiff and really hurt. I started to wonder why do I feel worse when I don't go to the gym? The answer: moving and stretching.
My body is so used to exercising that when I quit for a little bit, it stiffens up.
Here's a video from Dr. Berg that might help.
Get some vitamin D.