some things that may help
put the affected arm in a sling
fit tape from the top (point) of the affected shoulder pulling the shoulder back and slightly down. the tape should run at 45 degrees towards your spine
use a hot wheat bag (4 or 5 cups of wheat in a material bag and then heated in a microwave oven for about 2 mins) on the the muscle spasms or on your chest near your armpit.
tape a suitably soft pad (elongated that will run along your upper spine probably 2 inches in diameter) that will either stop you sleeping on your back or take pressure from the shoulder blade when you are sleeping.
gentle stretches of your head and neck at 45 degrees away from the affected shoulder blade eg move your head forward and to the left if the problem is on the right but never take your head back and towards the affected side.
a vibrating massager whilst you are laying on your front, on the muscles which run up and down either side of your spine.
dry needling (similar to accupunture) which can only be done by a professional
chiropractic corrections. good luck