What Causes Pain In Back,neck And Arms?

I am     having recurring pain throughout my back, neck, arms, and legs. It feels like which ever one hurts that day is being pinched and I can't get the pain to dtop. The section is also very tense. Yesterday and this morning it was the left side of my neck, this evening it's my left leg hip to foot. I cant sit for long periods of time with out feeling like a 70year old women about to use life alert. Im only 21.