Thanks for the query to H.C.M. Forum.
Let me explain , why there is pain in shoulder joint on left side ?
Why this pain relieve after burp ?
All these symptoms are related to each other .
As the nerve supply of shoulder joint( left) and diaphragm ( a membrane which separates thorax and abdomen from each other) which lies just above stomach is one and same .
So when there is distension in stomach due to gas formation it presses diaphragm and vagus nerve
irritate and this irritation develops pain in shoulder joint .
When burp gas release and pressure in stomach reduces hence no irritation of nerve , so no pain .
Hope I have answered your question and you understand it. If further any question I will reply.
Good luck. Dr. HET