Full Tilt $100 max NLH 9 handed table.

I'm in UTG+1 and get dealt A[s]Q[s]. UTG limps and I make it $5 to go. A guy 2 to me left calls and the limper calls.

Pot: $15
Flop: 4[s][5[s]4[d]

The limper bets $3 into the $15 pot. I don't want to start a raising war on the flop, so I just call it. MP caller calls it as well.

Pot: $24
Turn: 4[s]5[s]4[d]6[s]

First position checks, I bet $15, MP calls, checker folds. Heads up going into the river...

Pot: $54
River: 4[s]5[s]4[d]6[s]J[h]

I decide to bet $20 here. MP goes all in for $70-something total, so about $50 on top. $50 and some change for me to call into a $140 pot. What do you do?

I pound my fist on the table and fold. It looks like 55 to me.

I think he laid a nice trap if you called. 55

Actually, I thought that he might not make this raise without filling up, and as I was typing up the hand it looked more and more like it really should have been an easy fold. Why didn't I fold? *insert rant about how day had gone thus far here* I was likely tilting and tired of folding almost every time someone came over the top. In short I called and he turned over J[s]J[d]. I can't understand why he didn't raise the flop (though I figure to have overcards and a spade draw, meaning there are a lot of raises that I'd cal) and maybe he thought his J[s] would be good if he hit on the turn (though he didn't have odds to draw to it). I don't know, but I made a misplay and payed for it.