Hi, Im A 22 Yr Old Male. I Have Had

Hi, im a 22 yr old male. I have had a bump in the centre of my sternum above where the nipples are for a few months now. It started as a small, hard bump, slightly red and sore. After a month it seemed to go away and came back a little to the right. Then it was back in the middle of my sternum and grew a little, it was somewhat hard and sore. Recently it has begun to ooze puss and has begun to scab. What is it?