I have been looking to find a person with the same problem that I have. My back does the same way. Have you found out anything about yours? I kinda thought that it may be a nerve. I can also feel a sort of knot, but it doesnt feel like a knot knot , if that makes any sense.
Notalgia paresthetica is a little understood problem possibly caused from nerve root damage in C4-C7 and possibly long thoracic nerve damage. Pain grows progressively worse throughout the day. Furthermore, all reported exacerbation with activities requiring forward flexion of the arms such as driving, typing, washing dishes, or putting objects on a shelf. Read this and see if it fits. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2758879/
It does sound like a pinched nerve. I had a friend with the same problem as yours and he saw so many Drs. They could find nothing wrong so he started seeing a Chiropractor and the pain is gone. You may have to go several times because your body is used to your back being out of alignment in this area. My friend had to go 4 or 5 times and he feels great now. It's worth a try. Remar