Great turn gets raised in front of me

[imported_leader]

UTG is loose and passive
CO is a little tighter but generally passive post flop

Party Poker 3/6 Hold'em (6 max, 6 handed) converter

Preflop: Hero is Button with A[img]/images/graemlins/heart.gif[/img], 5[img]/images/graemlins/heart.gif[/img].
UTG calls, <font color="#666666">1 fold</font>, CO calls, Hero calls, SB completes, BB checks.

I probably should have raised PF here, you think?

Flop: (5 SB) 6[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(5 players)</font>
SB checks, BB checks, <font color="#CC3333">UTG bets</font>, CO calls, Hero calls, SB calls, BB folds.

I didn't want to inflate the pot here. Depending on the turn I was planning to call or raise.

Turn: (4.50 BB) 5[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">UTG bets</font>, <font color="#CC3333">CO raises</font>, Hero...

Holy crap! I hit the best card for my hand and now I got two passive players betting in to me. So what do I do?