Left Shoulder, elbow, wrist pain/discomfort after carrying heavy bags or walking dog? Hurts starting in shoulder blade. Uncomfortable.
Myofascial . This sounds like you may be experiencing a myofascial trigger point; this irritation of muscle groups can even mimic nerve root type pain. The shoulder girdle area is a common site for these types of regional muscle fiber strains. If your dog takes you for the walk (with lots of tugging) then a few trips to dog training school may help to change unruly tugging. A lighter, fashionista bag ?
Hard 2 say. With all these joints involved, look 4 something higher up, cervical or shoulder. Multi directional instability could B a cause especially if no injury. Pretty young 4 cervical arthritis. Could B a disk protrusion, especially if it runs in the family on the maternal side. These R just guesses, a hands on exam & perhaps imaging may B needed. Start with Ur PCP and B referred if needed. .