Why did you checkraise?

[sfer]

Party 20 game, 8 handed. CO posts. Folded to the CO who checks his option, I raise 22 on the button, unknown SB calls, BB folds, CO calls.

Flop is QQ4. Check/check, I bet, SB checkraises, CO folds, I call.

Turn is a 5. SB bets, I raise...