50-100 River bet or check?

[SoBeDude]

This is one of those heat of the moment decisions I usually get wrong, which annoys me to no end.

I'm new to the table. usual cast of characters.

UTG (27%, 11% PRF) raises, unknown in MP calls, I 3bet with red KK from the button. both blinds call.

Flop is Qc 5s 7h

SB bets, BB calls, UTG raises, MP reraises, I cap, ALL CALL.

Turn is 2d

checked to me I bet, ALL CALL

River is 6c

checked to me, I ...

Against 4 players, how often is a bet here with just one pair profitable?

Given this board, is this an autobet?

-Scott