Two pair gets check-raised twice - 400NL

[DaSpade]

Villain: 51/6/3 450h
Me: feeling rusty after an almost a month long break from poker

Party Poker No-Limit Hold'em, $ BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

saw flop|<font color="#C00000">saw showdown</font>

MP ($400)
CO ($241.60)
Hero ($394)
SB ($494.20)
BB ($500.26)
UTG ($412.54)

Preflop: Hero is Button with 6[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/spade.gif[/img]. SB posts a blind of $2.
UTG calls $4, MP calls $4, CO calls $4, Hero calls $4, <font color="#666666">1 fold</font>, BB checks.

Flop: ($22) 7[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(5 players)</font>
BB checks, UTG checks, MP checks, CO checks, <font color="#CC3333">Hero bets $18</font>, BB folds, UTG folds, MP folds, <font color="#CC3333">CO raises to $36</font>, Hero calls $18.

Turn: ($94) K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
CO checks, <font color="#CC3333">Hero bets $55</font>, <font color="#CC3333">CO raises to $110</font>