What Causes Pricking Pain On The Shoulders?

Feel like I am being stuck with a pin in between my shoulder blades. Started couple weeks ago. Goes away and then comes back. Could it be a pinched nerve from being at the computer all day. At first I thot I had a label tag irritating me, but it is a sharp prick. I found spot today by pressing and it was sore to touch. Then minutes later I couldn t find it. It moves down little bit and over to the middle of my back between shoulder as well. Forgot to mention that I am 63 years old, and had TIA one year ago. Have done great for one year on Plavix and Crestor (doctor just switched me this week to Lipitor because not as potent.....Cardiologist will probably be taking me off the Plavix and replacing with a 325 mg. aspirin. I ve done well on the meds for one year. No evidence of damage from the TIA but did have symptoms. Was hospitalized for 6 days until they discovered a P.F.O. - very small opening since birth I was told. Have had good year and Cardiologist will keep eye on it now that we know it s there. Now I have this annoying prick. I am 5 4 and weight 140 lbs. Please let me know your thots.