What Causes Red Knots All Over The Body?

my daughter is 14 she has been getting big hard red knots come up all over her body with a pimple in the middle almost like a spider bite when you mash it a LOT of yellow stuff comes out i have taken her to the doctor numerous times they will give her antibodics and a round of steriods but they will come right back with in a couple weeks after she is finished taking the medicine