Middle Pair from the BB

[Iridox]

I usually play NL SNGs but I'd like to learn how to actually play postflop poker, so I've started playing some limit again. I've read SSHE but I still feel like I'm a losing 1/2 player. I don't have any reads on the villain in this hand. Is my thinking ok or am I spewing chips?

Party Poker 1/2 Hold'em (10 handed) FTR converter on zerodivide.cx

Preflop: Hero is BB with A[img]/images/graemlins/diamond.gif[/img], 4[img]/images/graemlins/club.gif[/img].
<font color="#666666">3 folds</font>, MP1 calls, <font color="#666666">2 folds</font>, Button calls, SB completes, Hero checks.

Flop: (4 SB) 3[img]/images/graemlins/heart.gif[/img], J[img]/images/graemlins/club.gif[/img], 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(5 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP1 raises</font>, Button folds, SB folds, Hero calls.

Betting out is standard here, right? I'm not getting immediate odds to call the raise with five outs, but I think implied odds make the call ok.

Turn: (4 BB) 2[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks, <font color="#CC3333">MP1 bets</font>, Hero calls.

I picked up four more outs, so this call should be ok too.

River: (6 BB) T[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
Hero checks

I didn't improve, so I assume I have to fold if villain bets. I would be surprised if I'm good here 1/7 times, but I don't have a lot of experience.

Edit: I've been informed that betting out was awful and I now understand why, so you don't need to worry about that.