What do you do when you have medium stack and a guy keeps raising you after the flop (even if you raised before the flop) and you don't hit anything. you know he's probably bluffing most of the time but if you just rerais with nothing you risk that he's hit something this time?

Did he open on the flop, or did you check to him? What was his action PF? What hands has he shown down when he has down this action to other players?

Most of our encounters were when I'm on the SB and he's BB, either when I raised before the flop or called. I tried several times to open the flop even though I had nothing and he'd always come along and reraised on the next street. He won most hands without showing but when he did they were usually medium range like Q10, J9. Most of the times he had at list low or medium pair when he showed the hand.

You need to put him on a playable range based on his history, and adjust your play strategy accordingly. If you think he missed, then raise or bet.

ex. You raised from the SB, and he flat called. Flop comes AKQ, it probably missed him.

Don't be afraid to 3 bet if you think he's BS'ing you. But you need to weigh the EV of each move, and act on it.

Post up some (converted) Hand histories so we can over it in detail.