What Causes Sudden Tightening Sensation In The Chest?

I am having a tightening sensation...feels almost like a contraction in that it tightens and then releases but is not painful... in my right breast along the inner side and along the bottom. It is random and I cannot seem to relate it to any certain movement, activity, etc. I have had a biopsy in that same breast in the inner side over a year ago. It came back negative. I also have a place in the center of my back near my right shoulder blade that bothers me often, especially if I m standing along time. If you pushed that spot through to my chest it would be approximately in the same area as these breast spasms. I m wondering if there is an association with the two.