What Causes Red Pimple Like Bumps Around The Midriff?

I've been suffering from an outbreak of red pimple like bumps around my midriff but have seen one or two on my arm and side. They itch are pimple like and sometimes come to a white head. You can feel a larger bump under the skin. If they pop there is a yellowish white substance that comes out. When they go away they leave my skin discolored. Help!