but because you say the pains are not constant, it could be lungs, gas pains or just being muscular skeletal, the only way to know for sure is to go into see a doctor, additional questions and tests, I would start with a simple x-ray of the
shoulder and cervical spine. this will also give a high level picture of
gas, muscl strain etc... you should start there with a doctor and some blood work, ans some medical history. I would not worry to much until you have some evaluations completed.