Feels like it is going down from the skin to the bone - but that is a very, very small thickness, about .5-1cm. The pain that is in the breast rather than where the underwire in a bra is less painful, but is in the breast and not deeper.

I actually like the pulled muscle suggestion. I will warm the water up and have a nice hot shower and see if that helps at all. Odd thing is that I carry Liebling on my right side, so would have expected those muscles to pull first!