$.05/$.10, 6-max: How do I play this flop?

[Frank_In_Stein]

PokerStars 0.05/0.10 Hold'em (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is SB with 5[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img]. UTG posts a blind of $0.05.
UTG (poster) checks, MP calls, CO calls, Button calls, Hero completes, BB checks.

Flop: (6 SB) 5[img]/images/graemlins/spade.gif[/img], 6[img]/images/graemlins/diamond.gif[/img], 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(6 players)</font>
<font color="#CC3333">Hero bets</font>, BB calls, <font color="#CC3333">UTG raises</font>, MP folds, CO calls, Button folds, <font color="#CC3333">Hero...???</font>

Should I three-bet or just call? I believe I should slow down if any 3, 4, 8, 9 or diamond appears on the turn. Should I have check-raised the flop?