99 facing river raise

OK 10-handed Party 3/6 game. I limp 99 UTG, LP limps (about 35/6 VPIP/PFR), BB Checks.

Flop is Jd8d2h BB checks, I bet, LP calls, BB folds.

Turn is 4c, I bet, LP calls

River is 5s I think for several seconds, then bet, LP thinks for a good while and raises.

I don't remember any specific hands I've played with LP, however I do know that I have played a couple hands against him and played them very well (good value bets, good bluff pick-offs, and haven't lost a pot to him). I'm not really sure what to think of this river raise.