A flush draw against few players

[rafct]

suppose the following hand:

Hero is BB with 2[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/spade.gif[/img].

Only UTG, MP and button calls, and Hero checks.

Flop is K[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/heart.gif[/img], 3[img]/images/graemlins/spade.gif[/img]

Hero bets, UTG folds, MP folds, Button calls.

Turn is a 10[img]/images/graemlins/diamond.gif[/img].

I find myself new to this situation playing a flush draw against just one opponent. I was playing in a lower limit and before i would have many callers, so I would just check here, call a bet and hope to make my flush. Now that is heads up, how often should I be betting this? I find myself checking it and having to face a turn bet when the pot is small.
Thanks.