What Causes Pain In Shoulders?

Hi, my son (who is 17) about a week ago had a pain in his shoulders, the day after it hurt him to breath in, I took him to the doctors who couldn't find anything wrong apart from his pulse was high, he said if it didnt get anybetter in a few days to go back and see him, if he got worse over night take him straight to a&e. however he was fine, now for a day or two my son has been feeling really dizzy (even whilst sitting) he goes quite pale in colour and says he feels like he is having palpitations, he is also tired over the past few days.. any ideas?