Purple blisters on my kid's food and leg

Hi,

Two days ago my 3 year old complained her feet hurt.  Nothing was visible on her skin.  Later in the day two purple blisters formed, one on her heel and one on her leg.  The bases are red.  We took her to the doctor, who said it looked like some kind of infection and prescribed antibiotics.  He took a little fluid to be tested in lab and it will take a few days for the results to come back.  In the meanwhile, the kid is in good spirit, no fever, no loss of appetite.  She is complaining of pain from the blisters, but I cannot be certain whether it is because the blisters are painful, or because one is on the bottom of her foot and she steps on it which causes pain.

Just want to see if anyone out there had similar experience and what was the result.  I am feeling anxious waiting for the results from the doctor. 

Your comments are appreciated.