Child Having Flu Like Symptoms, Body Ache, No Improvement With Antibiotics. Further Treatment?

Hi... my little girl is 4 in february. She has been feeling ill for about 3wks now with flu like symptoms, runny nose tho most goes down to her chest which gives her an awful cough . She complains that her legs, back, tummy, throat , neck and eyes all hurt. Her fevers compound these symtoms which can get pretty frightening. We have had the usualladvice from our Gp plus antibiotics but in all this time there has been absolutely no improvement. She is usually a healthy and strong child and has no other medical problems. If you feel you could offer some further advice on this it would be very much appreciated