Hard, Black Seed Like Thing With Pus And Blood On Squeezing A Boil On The Back. Reason?

Over the past few days, a medium sized boil-like erruption with a very dark center has appeared in the center of my back in an area I cannot reach. It began to become uncomfortable, so after a shower, I asked my husband to take a look. He pressed around the area and a small amount of pus came out of center. As he continued to press, a very hard black seed-like thing popped out of the center of the boil. Then clear, bright red blood came out. We were most confused about the seed-like thing and what it could be. The pressure in my back has subsided and we put neosporin and a bandaid on it for healing . Any idea what the seed thing might be?