$200 NLHE 6-max: A3 makes straight, gets scary amount of action
I'm playing from the small blind at a 4 handed £1/2 live game in Reading, cutoff and button limp, I complete with A3, big blind checks. Flop comes down 245 giving me a straight and putting a flush draw on the board. I bet £4, BB raises to £15, cutoff calls, button makes a £70 overbet into a £42 pot. The table just opened and I've only played probably 5-7 hands with these people, but so far the BB seems like a competent player, cutoff a bit weak passive, button has been raising every other hand and monkeying a bit postflop, seems like he's here to gamble and show off.
I have £135 left behind when the action comes back to me and everyone has me covered, what's my play?