how do i play against players that just sat down?

[muckyouraces]

i run PA HUD while playing, and I believe I adjust pretty well using it. My biggest problem are situations like this. 6 handed: Player just sits down so i have played less than 5 hands with him (no hand history on him at all). I raise with a hand like KQo, someone flat calls and the new player flat calls. flop comes Q66 with a flush draw. New player bets pot into me, I call, turn, he bets the same amount as the flop, and river is same amount. by the time i call the last bet i have nearly stacked off w/ KQ because new player shows something like Q6. Should I just give the new player credit until I have some hand history on him? If i raise the flop, i have close to 65% of my stack invested so I can't really fold to a push can I? If I should ever fold, then when and why?