AK...need help

[BlackRain]

Villain (MP1) looked to be loose aggressive from my 30 minutes or so watching him on the table.

PokerStars No-Limit Hold'em, $0.25 BB (9 handed) converter

Hero ($19.75)
Button ($29.05)
SB ($34.05)
BB ($32.70)
UTG ($70.55)
UTG+1 ($42.50)
MP1 ($25.10)
MP2 ($25)
MP3 ($22)

Preflop: Hero is CO with A[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/spade.gif[/img].
<font color="#666666">2 folds</font>, MP1 calls $0.25, MP2 calls $0.25, <font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $1.5</font>, <font color="#666666">2 folds</font>, BB calls $1.25, MP1 calls $1.25, MP2 calls $1.25.

Flop: ($6.10) K[img]/images/graemlins/diamond.gif[/img], 4[img]/images/graemlins/club.gif[/img], 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
BB folds, MP1 checks, MP2 checks, <font color="#CC3333">Hero bets $3.5</font>, MP1 calls $3.50, MP2 folds.

Turn: ($13.10) J[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
MP1 checks, <font color="#CC3333">Hero bets $8</font>, <font color="#CC3333">MP1 raises to $16</font>, Hero calls $6.75 (All-In).

River: ($43.85) 9[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players, 1 all-in)</font>

Final Pot: $43.85

Results in white below: <font color="#FFFFFF">
MP1 has Js Kh (two pair, kings and jacks).
Hero has Ah Ks (two pair, kings and fours).
Outcome: MP1 wins $43.85. </font>

What should I have done differently? Looking back at this I think my flop bet should have been bigger. But I don't think LAG MP1 folds here even if it was pot sized.

I know I am just anticipating possible comments here, such as fold the turn. But this is my problem with poker. I can't understand why someone would call a 6xBB PF raise OOP with KJo. And I always seem to want to call to see the 3 outer suck out.

What do you do against players like this and any comments and criticism on my play would be great. thanks.