What Causes Soreness When I Sit Down On My Butt?

I have a question. I have noticed that its really sore when i try to sit down on my butt. The area is right at the top of my crack. I was looking in the mirror and i noticed that looks red and bruised. So i started looking and felt around the area and it kinda feels like i have a lump or something there and there is a red line going down my crack. I haven't did anything that would make it hurt like falling, getting hit, or anything. I just woke up and realized it hurts really bad.