Middle of back pain during TWW?

Ammie
Hey ladies,
So this morning is my 8 DPO and I woke up with pain around the middle of my back on both sides. It feels almost like overly worked muscles or something but I did nothing yesterday except go on a walk around the mall. Has anyone experienced this? I keep wracking my brains for anything I could have done out of the ordinary to cause it but keep coming up blank :/  thanks in advance for anything you share!