mole that comes and goes

Hi, almost a year ago i got three llittle flat dots on my lower back right next to each other, a few weeks later it turned into a black mole and got as big as the eraser of a pencil, it hurt really bad, few days later it started to bleed a little, not much just a little, then it size went down and the color changed to my skin color, few weeks later it came back again, hurt again, bleed again, its a repeat every few weeks, i dont have many moles on me, i have had two on me my whole like then last year this ont just came out of no where, im 24 years old, can someone please tell me any information then may know about this. thank you