What Are The Pus Filled Red Bumps On My Chest?

I have a rash that started about 5 days ago on my chest. Since then it has spread to my shoulders, upper back and neck. It started as small, red bumps that were raised a little and did not itch or hurt. Now it looks pimply and raised. It is tiny red bumps that look like they are filled with pus. I have also noticed that they have started to itch a little bit. What is this? How can I make it go away? Thanks!