Hello,
You may want to consider seeing another type of doctor. Some are more geared to work with muscular/skeletal concerns than others, like those geared toward sports medicine for instance. Having been through a similiar issue to yours (mine was likely caused by a 25 to 30 year old whiplash injury, & possibly scar tissue, from an accident, plus physical overwork). Sometimes a simple solution like alternating deep moist heat from a hotpack or a shower is enough, then switching to cold packs (if it feels like a muscle spasm) can work - or doing cold first then the heat may feel better for you.
You don't mention your age range, any upper body injuries or what type of work you do on a regular basis, but injuries aside - repetitive motion can also set up a certain amount of restriction in the range of motion, as can bad posture (I say that as I sit up straighter myself, LOL!).
You may want to look up exercises for this, which include moving the arms & shoulders & stretching them out - including pec stretches (front upper chest region), plus working on strength training can be key. Some of the videos on line show some great warmup sessions that can really help, as they are posted by everyone from chiropractors, physical therapists, personal trainers & yoga instructors. Bodyworkers who specialize in Myofascial Release or Structural Integration, or Active Isolated Stretching techniques can help too.
While that's no substitute for seeing a qualified doctor, you can gain some insight into other ways of helping yourself to regain your freedom of movement & reduce the pain you're having too. Good luck in clearing out the pain you've been having.