Turn semi-bluff gets re-raised!

[Rocco]

MP - Hero(33000)
CO(22000)
BB(15000)

I've been quite active lately due to a run of good cards. Have shown some of the in all-in situations and they've been rock solid cards like AA, AK, and QQ. CO seems aggressive and semi-loose...

It's a Party $5-rebuy with ~170 players left (money at 100) and average stack is around 20000...

Action (Blinds 500/1000):
Folded to me and I make it 3000 with K [img]/images/graemlins/diamond.gif[/img]J [img]/images/graemlins/spade.gif[/img]. CO and BB calls.

(Pot: 9800)
Flop: 4 [img]/images/graemlins/diamond.gif[/img], 8 [img]/images/graemlins/heart.gif[/img], 9 [img]/images/graemlins/diamond.gif[/img]

BB checks, I check (mistake?) and CO checks...

(Pot: 9800)
Turn: T [img]/images/graemlins/diamond.gif[/img]

BB checks, Hero bets 5700, CO goes all-in for the rest of his ~18000... BB folds... What to do? I have flush draw, straight draw and two over-cards. I might be drawing dead to a nut flush, but would he really go all-in with a made flush here? My overcards is probably not winning outs. Could he also be making a semi-bluff with the A [img]/images/graemlins/diamond.gif[/img]? Call or fold?