(NL5) Hero flops idiot end - but is his play retarded?

[BotOnTilt]

No reads on villain, this is his third hand.

No-Limit Hold'em, $0.04 BB (10 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

CO ($5.36)
Button ($0.82)
SB ($5.32)
Hero ($5)
UTG ($4.47)
UTG+1 ($1.54)
UTG+2 ($4.44)
MP1 ($2.24)
MP2 ($6.07)
MP3 ($4.92)

Preflop: Hero is BB with A[img]/images/graemlins/club.gif[/img], 2[img]/images/graemlins/diamond.gif[/img].
UTG calls $0.04, <font color="#666666">1 fold</font>, UTG+2 calls $0.04, MP1 calls $0.04, MP2 calls $0.04, MP3 calls $0.04, <font color="#666666">2 folds</font>, SB completes, Hero checks.

Flop: ($0.30) 4[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/spade.gif[/img], 3[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(7 players)</font>
<font color="#CC3333">SB bets $0.04</font>, <font color="#CC3333">Hero raises to $0.3</font>, UTG calls $0.30, UTG+2 folds, MP1 folds, MP2 folds, MP3 folds, SB calls $0.26.

I hate playing ace-rag, since its so hard to win anything with it as its so overplayed at NL5. But now hero has a straight, and I bet to protect my hand.

Turn: ($1.20) 3[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets $1.1</font>, UTG calls $1.10, SB folds.

Didn't expect to see so many callers on the flop, and the pot is huge now. Can't expect my hand to be any worse even though the board is paired. If someone has a full they would probably let me know.

River: ($3.40) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">UTG bets $1.96</font>, Hero ??

I checked the river, since the flush card came. But also because a thinking villain should probably assume that I have a full house, right? I was expecting a cheap show down but will not get it. My straight can't be any good now, can it? With the two pairs on board and the flush all I can beat is an over pair. An over pair wouldn't be out of the question since its UTG and a weak player might use my check as an invitation to bluff, still that board is a scary as it can be for my straight. Should I have played it differently? And there is no way I can call the river, right?