in over my head

[piggity]

So I find myself sitting in a 1/2 game again, feeling somewhat over-matched aside from two obvious weak spots. The villain here is a TAG, possibly a pro, and probably views me as weak. Earlier he opened on the button, I defended my BB with KTo, c/c a low paired flop, c/r T turn, bet out Q river and won the pot (he called river but did not show his hand -- but he did show his neighbor and the ensuing conversation suggested he had flopped a low pair with a K kicker).

So obviously he's raising with a wide range OTB -- but just how wide can I assume that range to be?

Anyhow we're 7 handed at the moment and he open raises on the button again, SB folds. I have A7o in the BB. Now is this a mandatory 3-bet?

I just call, and the flop is KQxr. Can I just c/f here or am I just giving away money by playing this way?

Thanks in advance for any thoughts.