If you can lay on your stomach with a pillow under your hips, you may get some relief and once relaxed, your back may “unlock”. Without being able to do a physical assessment I can’t really give you much more actionable advice. Try to normalize movement and deep breathing. Often the muscle tightness is your body bracing against a disfunction so if you can move as normally as possible the automatic bracing may be reduced allowing your vertebrae to return to normal positioning.