I call and check on the next street (unless I trip up on board) since my Qs and suit are live AND you don't know this opponent. My guess, based on the betting, is you're up against a set or a higher pair in the pocket (probably Aces if their was that much raising on 3rd st), but again because you're not sure of this oppponent, it could also be a free card play, a low pair with a Q in the hole as DrK suggested, or, it could be a clueless individual with 4 to the flush in a dead suit, or even 4 to a gutshot straight....you almost have to call to the river. It sucks, but you also might take the hand.