I have a lump on the right side of my right butt cheek. I am 16 years old, turning 17. it is about the size of a grape, and only hurts when I walk or apply the slightest pressure to it. it has been there for the past 3-4 weeks. sometimes I find it to be bigger, other times it is smaller and does not hurt as much. I have not told anyone anything about it. what could this be? could it be cancerous? is it harmless? Also, about a week ago, i noticed the skin around getting loose and "thin". 3 days ago, when i woke up, it burst and lots of blood and a little bit of "white stuff" came out.