I don't really know how to set it up.

UTG has been aggressive on middle streets, but then open folds river several times.

PokerStars 0.25/0.50 Hold'em (10 handed) Poker-Stars Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

Preflop: Hero is MP1 with 9, 9. CO posts a blind of $0.25.
UTG calls, UTG+1 calls, UTG+2 calls, Hero calls, 2 folds, CO (poster) checks, Button calls, SB completes, BB checks.

Flop: (8 SB) 6, 4, 2 (8 players)
SB checks, BB bets, UTG raises, UTG+1 folds, UTG+2 folds, Hero 3-bets, CO folds, Button folds, SB folds, BB calls, UTG caps, Hero calls, BB calls.

Turn: (10 BB) 9 (3 players)
BB checks, UTG bets, Hero raises, BB folds, UTG 3-bets, Hero calls.

River: (16 BB) Q (2 players)
UTG bets, Hero raises, UTG 3-bets, Hero calls.

Final Pot: 22 BB

If you're gonna raise the river, just cap the turn, and call the river if he leads.

why just call the turn if youre going to raise the river?

Are you limping this preflop?

and I agree with the advice given above.

No, value raise preflop.

I think this is the mistake I made in the hand. I should have put another bet in on turn.

During the hand, I realized on the river that the flop action didn't jive with a flush draw so I put another bet in.

UTG could easily have a combo draw on the flop, and got there with the flush on the turn. 78h, 57h, etc, or could have gone nutso on the flop with fd+overs, etc, which isn't necessarily out of line.

At the same time, he could have AA or something that he limped UTG and wants to jam now, lol.