from the description of your pain, i would like to do a neck xray to rule out cervical spondylosis
which can make you to have pain in the shoulder and back area as the nerves that are present come from the neck.
i would also like to rule out any problems in the tummy as the shoulder pain
can be a referred pain
from the tummy need to rule out causes like pancreatitis
, gastritis, gall stones
, cancer of any organ etc.
would also rule out heart problem by doing ecg as well as the pain is in the left shoulder area.
get an ultrasound done to rule out any any problem in the abdomen
i would suggest that you see a physician for a proper checkup and further treatment.
get well soon and takecare.