Lots of water.

Magnesium.

Take 100 deep breaths, consciously relaxing your body with each breath out, pretty soon you will start to notice muscles guarding other sore muscles, and you can relax them and work on relaxing the problem area.

Various back and neck stretches.  You can try the broomstick stretch, you hold a broom parallel to the floor in front of you with both hands, then pivot your shoulders to raise your hands over your head like you are doing a pull-up.  Should stretch the area in between the shoulder blades.  You can do gentle head circles and arm circles.  Sit in a chair and hold the seat to the side with one arm and stretch your neck to the opposite side to stretch the muscles.

Try a foam roller or a ma roller on your back.

When I get pain like you are describing, my C6 or C7 vertebra is out. When I run a tillage tool and look behind a lot, actually two of my upper cervical vertebra get counterrotated.