QJ oop on Q33 board

[Fathomer1977]

CO is new to the table. Nothing difficult about the hand but at a loss as to how to interpret his calling down.

Full Tilt Poker, $0.05/$0.10 NL Hold'em Cash Game, 6 Players
LeggoPoker.com - Hand History Converter

Hero (BB): $3.65
UTG: $4.95
MP: $4.30
CO: $6.95
BTN: $2.75
SB: $2.95

CO posts $0.10
Pre-Flop: J[img]/images/graemlins/club.gif[/img] Q[img]/images/graemlins/heart.gif[/img] dealt to Hero (BB)
UTG folds, MP calls $0.10, CO checks, BTN folds, SB calls $0.05, Hero checks

Flop: ($0.40) 3[img]/images/graemlins/heart.gif[/img] Q[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/diamond.gif[/img] (4 Players)
SB checks, <font color="red">Hero bets $0.25</font>, MP folds, CO calls $0.25, SB folds

No draws on the board. He posted so there's no range for his preflop hand. I'm thinking he's slow playing the 3, has a Q with a weak kicker, or has an A. Is this a correct analysis?

Turn: ($0.90) K[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">Hero bets $0.50</font>, CO calls $0.50

River: ($1.90) 7[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">Hero ?</font>,