I have pain in my shoulder that comes every couple of minutes and is relieved by belching. what could this be?

Without knowing: More details it is hard to say specifically. Could simply be gas with referred pain to the shoulder. Obviously if you have other symptoms (tight chest, sweating, arm/neck pain, etc) you should call 911.

Diaphragm inflamed: An inflamed diaphragm may cause referred pain to the shoulder. Your belching suggests an abdominal cause such as gallbladder/liver (right shoulder) or stomach/spleen (left shoulder) but there may be many other causes you should discuss with your internist if it persists. As stated, it could also be a sign of heart disease, in which case you should call 911 if urgent or consider a stress test.