Full Tilt No-Limit Hold'em Tournament, 150/300 Blinds 25 Ante (9 handed)

UTG (t8455)
UTG+1 (t17980)
MP1 (t6795)
MP2 (t13046)
Hero (MP3) (t5440)
CO (t9064)
Button (t10700)
SB (t16095)
BB (t20040)

Preflop: Hero is MP3 with A, Q
2 folds, MP1 calls t300, 1 fold, Hero bets t1500, CO calls t1500, 4 folds

Flop: (t3975) Q, 3, 3 (2 players)
Hero bets t1200, CO raises to t4000, Hero calls t2715 (All-In)

Turn: (t11805) 4 (2 players, 1 all-in)

River: (t11805) 5 (2 players, 1 all-in)

Total pot: t11805

Hero had A, Q (two pair, Queens and threes).
CO had K, K (flush, King high).
Outcome: CO won t11805

I bet and then went-all in on the flop because I thought that if CO had had a better hand (AA or KK) he/she would have raised pre-flop. Instead I got tricked (or is it usual in tournaments?). Any advice is highly appreciated.