Why

I don't know why but I like doing mean and cruel things alot. But I also like doing nice things a lot. And I don't know why heck when I was about 11 or 12 I could do tons of bad and mean things and not feel bad about it and I stayed that way but when I turned 18 I couldn't do something mean without feeling bad about what i did and i notice the more I go to church and do good stuff like that the worse I feel about the bad things I do. I am still trying to figure out why this is happening to me. If anybody has any idea's as to what i should do please feel free to tell me.