What Causes Welps With Hard Center In Leg & Foot?

my 2 1/2 yr old went to doctor yesterday with an infection on her left leg and a possible insect bite on her right foot that was swollen, red and warm to touch. the doctor said it was probably impetigo and prescribed her antibiotics orally and a cream antibiotics. today she started get quarter size welps that are non itchy and with a hard center on the leg with the swollen foot. could you possibly tell me what the welps could be. there are about ten of them throughout her whole leg