What Causes Severe Pain In Left Rib Cage?

Question : I have been having pain in my left rib cage- started going to Chiro and seeing some lots of improvement. Last Wednesday, upon completing the nerve stimulator therapy, when I stood up I had an immediate pain in my lower left breast/ interior to cleavage area. Completed the adjustment and the pain continued to get worse throughout the evening- radiating in my left breast. Friday, I went back to the chiro and the adjustment helped a little but there is a specific area of my breast that is sore to the touch. It hurts with a bra on, sports bra on, off, laying down and walking (from the impact of walking). It is sore to the touch and I can see some difference based on movements of my arm, posture, etc. Today, the pain began radiating to my left shoulder down to arm/fingers and a little on my right shoulder. Hot shower helps the pain and overall I feel that the pain is not constant like it was earlier this weekend. Yesterday was the last day of my menstral cycle and I have changed thyroid dosages as of March 16th due to low levels and have begun B12 shots (2 shots to date, each week). I am thinking that this is likely a pulled chest muscle, trying to determine iif this one "spot" hurting is typical for this type of issue. I do have a routine mamamogram scheduled for April 9th but until then need to get some peace of mind.