Alot of times this can be a symptom of gall stones. I would recommend seeing your doctor, discussing the problems you are having and asking for a gall bladder ultrasound. If this is negative, then I would ask for a CT or an MRI of your shoulder. Also you can have him/her check your Amylase and Lipase levels to check for problems with the gall bladder. The gall bladder pain can start in the middle of your chest, through and under your ribs, and all the way to your back where the shoulder blade is, causing it to hurt when breathing. I would have this checked out as soon as possible because if this is a gall bladder problem, you do not need it rupturing. Hope this helps and good luck.
I had a pain just like that... and when I tried to pick up anything it would run down my arm and cause numbness... I ended up having a medial branch nerve block done by my pain management doctor.... the pain was coming from my lumbar spine and once I had the procedure done the pain went away and has not returned... the procedure was a number of years ago. Maybe yours is something similar.... good luck... hope the info helps.