What Causes Pain In Shoulder Radiating To The Back Of Neck?

Hi, after I eat I have a feeling of pain in my right shoulder and if the pain is severe it radiates to my back-my shoulder blade- and my neck.The pain started very mild a year ago and only happened after breakfast but now in the past month it has become severe and constant(after every meal and even in between the meals). In the last month I have also a feeling of very strong movements and fluttering in my stomach about 1-5 minutes after eating. My doctor checked my heart due to the nature of the pain, X-rayed the lung and gave me stomach acid re flux pills. My heart and lung tests were all normal and stomach pills made no difference. What may this pain be due to?