What Causes A Painful Lump On The Labia?

This morning I woke up and when I moved a felt a small stabbing pain in my labia. When I get in the shower I tried to check it out and I found a nickel sized lump in my labia that is quite painful when touched. I have never had this before and I am really concerned as to what is is. I used a tampon for the first time last night. I don't know if that has any connection.