About a week ago i had all these small red bumps behind my knee, at that time they were itchy. Since then the bumps have changed slightly to have a little read head, like the head of a pimple and they're no longer itchy, they hurt, almost like a burning. They haven't grown in size or in number and they are only behind the one knee and not elsewhere on my body. Any clues as to what this could be or how to take care of it would be much appreciated!!