Persistent diarrhoea and coughing?

my little girl will be one years old this week saturday.... for the past few months she has had a horrible cough.... very phlegm and often makes her vomit. She also seems to have constantly runny poo, to the point where it comes out of the nappy and sometimes she goes 5 to 6 times a day. i have taken her to the doctor several times about this but they keep sending me away saying that her chest is clear and the diarrhoea will clear itself up... has anyone had this before. could she be coughing on purpose to get my attention or something..