Does Pain From Armpit To Shoulder, Neck And Arm Indicate Pinched Nerve?

i woke from a short nap to excrutiating pain from my lower under arm pit area to my shoulder, neck and all the way down my arm on my left side. There are short periods of relief, but mostly constant, and worsens when I lay down. Is this a piched nerve? There has not been any trauma involved, and it is now been 3 weeks with no signs of healing.