PokerStars 0.10/0.20 Hold'em (8 handed) from (Format: FlopTurnRiver)

Preflop: Hero is MP2 with 9, 9.
3 folds, Hero raises, 2 folds, SB calls, 1 fold.

Ok, I thought this was a typical open raise ("if it's folded to you and it's good enough to open with, it's good enough to raise with" or something like that)....Table had been unusually tight so I expected it to be folded around.

Flop: (5 SB) 7, A, 2 (2 players)
SB bets, Hero raises, SB calls.

SB was somebody I had (about 4 hands earlier) caught bluffing when I hit quads on a board of 5535 (I had 5x from the BB). he had called down with K4o. He had raised my flop bet and just called when i insta 3bet that flop...Not giving him a lot of credit for a hand here (he'd also played quite a few hands)

Turn: (4.50 BB) Q (2 players)
SB checks, Hero bets, SB calls.

River: (6.50 BB) 7 (2 players)
SB checks, Hero ???

At this point, I kind of feel like I should bet out, but I also feel that with the A and Q on the board I may be in trouble...comments?

You are insane if you bet here. It goes beyond spewing - I may have to come over and kick your ass if you bet here. And then burn your house down.
If you bet this river, 100 puppies all die.
etc
etc
etc

Hell, I am not sure I like the turn bet. Most donks who weak lead into a preflop raiser (which is the technical term for what he did) has top pair/bad kicker or a flush draw (which got there).
But as long as you insta-fold to a checkraise it is decent.
But you might be better off just picking off a bluff on the river after checking the turn given the description you gave (not advocating this line against anyone).
Just remember- sometimes you gotta cut your losses even against donks.