Dawn - it sounds alot like when my rhomboids get strained.
Here's a link with pics of where they are-
http://images.google.com/images?um=1...en&q=rhomboids


the thing is they are a weak muscle and easiy over stretched/strained .
so I found when mine start hurting I need to really be aware of bringing my shoulders back and doing little squeezes or isometrics to "pump" them back into shape.

basically for me that pain/ache means I have not been good enough with my posture.

I hope the pics help you to figure out if it is the cause of your new pain.