Hurt my hand in a fight, please help!?

hiya please help me, i was having a fight yesterday with my best friends ex and he threw me on the road so i hit him around ten times quite hard, and now my knuckle ( not the ones on fingers, the one on hand ) is exreamly sore, its aching,a little tiny bit swollen,and a little bit bruised, it hurts when i try to write, and i cant clench my fist without it really hurting, what have i done to it? thanks xxxx