Why does my dad hit me all the time?

i'm 15 and he only used to do it as a punishment...but now i think he just does it when he's bored, what can I do about it? I know I should call the cops but I don't want to go to a foster home cause I won't be able to see my son(I know that really young to have a kid) or my girlfriend, and I can't live with my mom cause I don't know where the **** she is...so what should I do?(I'm a guy)