What Could Bruised Elbow With Swelling Suggest?

i fell off while riding a bike and had a bruised elbow. it healed in three weeks and i started going to gym as before. but now the area were i was hurt is little swollen and has become dark(kind of black). also the wound opened a bit and now the skin there has become extra soft. should i consider taking another course of antibiotics ? i feel there's puss forming inside the wound. please help