why can't i earn EXP on halo 3 online?

[ratliff.granite]

i have been playing halo 3 online for a good period of time, but my EXP won't increase. i have heard that when you win a game your EXP increases but i have won many games and it is still at EXP: 0. my skill however has increased among the games and it is now at 7. why can't i earn EXP online?

 

[farah f]

you have to win or become mvp in rank or social games