I Have Had A Really Sharp Pain In My Back

I have had a really sharp pain in my back area upper left side.it travels from my front to back.mostly the back. If I cough or sneeze it really doubles me over. Ive had no trauma to the area or lifted anything too heavy. if I lift my left arm above my shoulder it is painfull. if I sit still or lay on my back there is no constant pain. This has been going on for 4 days now and is kind of worrying me. Its like there is an ice pick behind my left shoulder blade jabbing me everytime I get up or move my arm.