Suggest Treatment For A Pimple Behind The Ear Lobe

Red pimple like spot behind my earlobe. It has been there for a while as I had attempted to pop it and was unsuccessfull. Yesterday out of the blue, it started bleeding and what looked to be a mixture of pus as well. It appeared it had deflated a little bit once it stopped, but there was still a spot there today. I preceding to pop it and a bunch of pus came out that had a terrible odor. What is causing this?