I have these hard, gray balls/bumps under my skin. It feels like a tiny bead under the skin. They are small, about quarter of a centimeter in diameter. I have them on my hips, butt, torso along rips, and the underside of my forearms and behind my knees. They can't be popped. If you cut into them or puncture, pus comes that appears to contain tiny hairs or fibers. They don't go away with exfoliating or acne products. What could these bumps be and how can I get rid of them?