My piercing is really infected. What should I do?

I got my cartilage pierced back in February, it was done with a piercing gun. Anyway, it always hurt and burned a bit. I cleaned it like I was told to do and took good care of it. I have both my nose and belly button pierced and I never had problems with them healing. A couple weeks ago, I was getting ready to go out and my friend was doing my hair. My friend accidently snagged the brush on my piercing, which hurt really bad. This morning I noticed there was a big red bump underneath my jewelry, so I took it out. I think the bump is filled with puss.. I'm not really sure what I'm supposed to do. Is this serious? Or will it go away on it's own?