Could easily be AA AK or KK.

Since you are in position i would probably raise the flop and see if he was just continuing. If he raises or calls then leads out again on the turn, you're way beat.

His turn bet is small but it could be because he doesn't want to let you off the hand. Without having raised the flop it's hard to say if he is weak or really strong.

River bet is the same size, which is small compared to the pot at this point. Going all in on the river here accomplishes nothing though. There is no worse hand that is going to call you, and no better hand that you are going to be able to make lay down. At this point i think you can't fold because the bet is so small compared to the pot and villain might be full of crap, so just call the river and show it down, but i think you're beat here.