Raised on the river...

[jakbse]

SB is unknown. I have been away from poker for a month and didn't really know what to do here.

Party Poker 0.50/1 Hold'em (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is BB with A[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/club.gif[/img].
UTG calls, MP calls, <font color="#666666">2 folds</font>, SB completes, Hero checks.

Flop: (4 SB) 7[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero checks, UTG checks, MP checks.

Turn: (2 BB) A[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, UTG folds, MP calls, SB calls.

River: (5 BB) 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, MP calls, <font color="#CC3333">SB raises</font>, Hero?

I think it is quite unlikely this river helped him, but a bluff raise seems even more unlikely against two players.
What's your play?