Big Pot, Call river bet?

[zPro]

READS
UTG: Just sat down, no reads
MP: Passive... few hands ago he donk bluff bet the turn into the flop bettor
SB: DONATOR, super loose PF, very loose calls postflop, calls down with anything


Absolute Poker 0.50/1 Hold'em (6 handed) converter

Preflop: Hero is Button with T[img]/images/graemlins/heart.gif[/img], T[img]/images/graemlins/diamond.gif[/img].
UTG calls, MP calls, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises</font>, SB calls, <font color="#666666">1 fold</font>, <font color="#CC3333">UTG 3-bets</font>, MP calls, <font color="#CC3333">Hero caps</font>, SB calls, UTG calls, MP calls.

I raised this because I knew the SB would call. I did have UTG on AA or KK as a possibility (no reads on him).
Good or bad?

Flop: (18 SB) 5[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/club.gif[/img], 6[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">UTG bets</font>, MP calls, <font color="#CC3333">Hero raises</font>, SB calls, UTG calls, MP calls.

Turn: (13 BB) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, UTG checks, <font color="#CC3333">MP bets</font>, <font color="#CC3333">Hero raises</font>, SB calls, UTG calls, MP calls.

River: (21 BB) 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, UTG checks, <font color="#CC3333">MP bets</font>, Hero ???, SB and UTG left to act.

My first immediate reaction was to fold, and I didn't like being right behind the river bettor with 2 players behind me. The pot was insanely large. I didn't get 3bet at the turn, so I figured there's a small chance my hand is good.

Comments on all streets appreciated.