Villain has been spewing chips all over the place since I sat down - running at 41/12/4.7. I had 3 bet his last 3 raises to isolate with AJs type hands and took them down on the flop all three times. This is my 4th 3-bet in quick succession. How do I approach the flop, I think bet sizing is key.

PokerStars No-Limit Hold'em, $0.25 BB (4 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Hero ($54.80)
UTG ($9.80)
Button ($25)
SB ($34.45)

Preflop: Hero is BB with A, A.
2 folds, SB raises to $1, Hero raises to $3, SB raises to $10.5, Hero calls $7.50.

Flop: ($21) 3, J, 8 (2 players)
SB checks, Hero bets X?