Help! There's a tiny lump between my little and ring finger knuckle after they swelled from punching in karate?

Well it's not the finger but the knuckle that's the problem but that's not an option for the topic thing...
So I punched something really hard during karate and my little finger and ring finger area turned very purple and blue, and the bruising spread down my hand. The two knuckles also swelled up a lot and it hurt a lot at first but after two days it was just a constant irritating throb.
It's two weeks later and the swelling and bruising is completely gone, but as the swelling went down I noticed a small lump of something between my little and ring finger knuckle. It's very small, probably about half a centimetre, and I know it shouldn't be there. It's hard but I can't tell exactly how hard as there is a little skin and flesh covering it so it's difficult to tell completely. It's between the knuckles but a little bit forward and it hurts when I put pressure on it with my hand in a fist (like if I do push-ups with fists)
Please help! I completely ignored it and let the swelling go down by itself, which I am now regretting and I am worried this could be quite bad.