also you bet 3 into a $9 pot (not accounting for rake).. which is pretty weak, he may have sensed a weakness and raised you for that reason. I do this to alot of people. I'm a pretty aggressive player post flop though, you need a good player read.

I posted this hand on another thread so you may have seen it.. but as an example of a way i did to someone what he may have done to you...

POKERSTARS GAME #2426634102: HOLD'EM NO LIMIT ($0.25/$0.50) - 2005/08/26 - 11:11:16 (ET)
Table 'Silesia' Seat #4 is the button
Seat 1: Biff ($12.50 in chips)
Seat 2: Stag Man ($19.60 in chips)
Seat 3: ManlyMan ($52.20 in chips)
Seat 4: Scott Owen ($76.85 in chips)
Seat 5: LouieTheBook ($66.80 in chips)
Seat 6: doc3232 ($21.50 in chips)
Seat 7: 90 Corvette ($86.05 in chips)
Seat 9: howley22 ($26.50 in chips)
LouieTheBook: posts small blind $0.25
doc3232: posts big blind $0.50
marcsavard27: sits out
*** HOLE CARDS ***
Dealt to Scott Owen [Qh Ac]
90 Corvette: raises $1.50 to $2
howley22: calls $2
Biff: folds
Stag Man: folds
ManlyMan has timed out
ManlyMan: folds
ManlyMan is sitting out
Scott Owen: calls $2
LouieTheBook: folds
doc3232: folds
*** FLOP *** [7c 5c 2h]
90 Corvette: bets $3
howley22: folds
Scott Owen: calls $3
*** TURN *** [7c 5c 2h] [Js]
90 Corvette: bets $5
Scott Owen: raises $15 to $20
90 Corvette: folds
Scott Owen collected $21.65 from pot
Scott Owen: shows [Qh Ac] (high card Ace)
*** SUMMARY ***
Total pot $22.75 | Rake $1.10
Board [7c 5c 2h Js]
Seat 1: Biff folded before Flop (didn't bet)
Seat 2: Stag Man folded before Flop (didn't bet)
Seat 3: ManlyMan folded before Flop (didn't bet)
Seat 4: Scott Owen (button) collected ($21.65)

obviously you need a read to justify calling/raising though... but if you were to bet more on the turn you'd have better info, if you bet $6-7 into $9 and he still raises you, he has a hand.