sharp pain on arms

Hello, I'm 33 yrs. old and i've experienced a sharp pain on my arm, right below my shoulder.  It's either the left or right side.  It's a sharp stabbing pain that comes and goes.  I sometimes suffer from anxiety and i've had an ekg, about a 1 1/2 ago and it was normal.  This pains i've had them on and off for about more than a year. I've mentioned it to the doctor and he said that maybe i've strained my arm, or that i'm doing some kind of movement that's making it hurt, but sometimes out of nowhere i get this pain.  I'm just wondering if anyone has ever felt this?  Does it have to do with the heart or something else?

P/s I'm not overweight nor have other health problems that i know of. I also exercise regularly.