The SB 3bets you preflop you 4bet, and now he bets into 2 players, a fish and a preflop 4 bettor, on an Ace high flop. This is a sign of great strength IMO. In this situation I would also just call on the flop as you did. In fact, I would not put in a single raise postflop unless I improve, I would just call this down. My goal here would be to get to the showdown as cheaply as possible.