TMI weird bump on my butt

Like I've had that bump for a really long time but it hasn't hurt until now. I touched it while putting lotion on and it hurt really baadd.?Its a really sharp and short pain.Does anyone know what this could be. Yes i am sexually active. The last time i had unprotected sex was in August. But what kind of std affects your ass crack???
Update: i kept touching it and i think its bleeding