Hi, This Morning I Was Hanging An Item Of Clothing

Hi, This morning I was hanging an item of clothing (not stretching) on the clothes line. when i put my arms down I got this instant shooting pain right across the top half of my back. 2 hours later the pain is still there, even if i don't move. I can feel it when i breathe. it runs right across the back but most of the pain is in the middle of the back.