99 on kk6 flop heads up

[cocofrite]

PokerStars 30/60 Hold'em (8 handed) internettexasholdem.com

Preflop: Hero is BB with 9[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/heart.gif[/img].
<font color="#666666">6 folds</font>, SB completes, <font color="#CC3333">Hero raises</font>, SB calls.

Flop: (4 SB) K[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/diamond.gif[/img], 6[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">SB raises</font>, <font color="#CC3333">Hero 3-bets</font>, <font color="#CC3333">SB caps</font>, Hero calls.

Turn: (6 BB) 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets</font>, Hero calls.

River: (8 BB) K[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets</font>, <font color="#CC3333">Hero raises</font>, <font color="#CC3333">SB 3-bets</font>, Hero calls.

Final Pot: 14 BB

villain is very agressive.
if it was against someone more solid, I'd fold turn.
what do you do against unknown ?
if you call the turn, do you just call river ?
can you find a river fold after my raise ?