10/20 - Protecting my hand in a big pot, taking it too far?

[spamuell]

At the time I played this hand I didn't know the opponents that well yet but I knew UTG was limping with lots of trash (which made me more reluctant to do this on the turn) and that the button was quite loose and aggro.

Party Poker 10/20 Hold'em (6 max, 5 handed) converter

Preflop: Hero is SB with A[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/heart.gif[/img].
UTG calls, <font color="#CC3333">MP raises</font>, Button calls, Hero calls, <font color="#666666">1 fold</font>, UTG calls.

Flop: (9 SB) 2[img]/images/graemlins/heart.gif[/img], 3[img]/images/graemlins/spade.gif[/img], T[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">UTG raises</font>, MP calls, <font color="#CC3333">Button 3-bets</font>, Hero calls, UTG calls, MP calls.

Turn: (10.50 BB) 6[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
Hero checks, UTG checks, MP checks, <font color="#CC3333">Button bets</font>, <font color="#CC3333">Hero raises</font>

I'm almost always behind here aren't I? Is it worth the extra bet to protect my hand the times I'm not? Also there's a chance that UTG will fold 77-99 or even a weak T and that button is just betting because it's a huge pot and it was checked to him (EDIT: Ok, he 3-bet the flop, there isn't really. But the pot is so big, I still think this might be worth it). I'm not desperately worried about MP, I can't see him checking an overpair on the turn and I figure that if he was slowplaying something then 2 bets are probably going in on the turn anyway but unless he has TT then not three.
Comments?