Why do i not feel guilt or emotion?

the other weekend i saw this kid who had this cool gold chain and i told him to giv it to me and he said no so i grabbed a brick and smashed him over the head then he immediately dropped and i threw the brick at his head. i am only 15 and when someone asked how i got that chain they said theyd feel sick if they done that to someone but if anything i found it sort of funny. and when i get into fights, sometimes i cant stop hitting them and im pretty sure one person i bashed was on the news and was in a coma. ive even taken bikes off little kids and punched them when they look about 10 and still dont feel bad. is there something wrong with me and can i change