Hi. i am a medical doctor and i read your post . if your shoulder pain is following a movement then it is more muscle or ligament related,if it is sharp and comes suddenly and when sleeping or after heavy meal it is more probably from stones in gallbladder, The chronic cough after eating is probably from acid reflux . you can do the Xray but lung cancer is least probable, because you are young and you don't have risk factors. first thing you should do is abdominal ultrasound and avoid fatty meals and oil especially at night and take anti acids or proton pump inhibitors before meal for acid reflux and you should keep on diet and exercise.