My son who is 9 years old has had the flu, sneezing runny/congested nose, persistent cough that caused him to throw up 3 or 4 times over a 2 day period, high fever for about 3 days. His symptoms have improved, he hasn't run a fever for more than 24 hours now, however he is complaining of stiff soreness running down the back of the legs, he feels really weak and has diarrhoea and still feels like he wants to vomit but doesn't. Not sure if I wait or take him to the GP? Could this be developing into something else?