Black thing on skin!!! PLEASE HELP!!!?

okay so about a week ago I noticed a pimple like black thing on my skin, it was dome shaped and it felt uncomfortable when I touched it. aabout 7-10 days later today I was sitting on a bench and I scrapped it accidentaly and it started hurting kinda like a sliver, so me and my friend started it squeezing it out like a pimple, it looked like a pimple ready to come out. It was rather large, kinda like a g seed, under some pus and blood it finally came out! Now I have a spot on my skin the size of the black thing, and the hole is black (kinda like after a pimple) but this one actually left a black stain like after being stabbed with a led pencil. I just got it out, and my back hurts in that area, and it kinda goes into my arm. I disinfected it and put a bandade on, im really scared WHAT IS THISS!!!??? 10 pointtss! i promiiisee??!!