Common situation :99 donked on flop

[Erik W]

Just sat down. No reads.

I raise 99 in MP. Both blinds call.

Flop: 56Qr

I get donked by BB. Hero...

Which are the lines you take here.
Which lines against different opponents?

If I have seen Villain donk with second pair I raise this and bet turn and might bet river too.

I take this to showdown way too often, I think. It feels I'm spewing 2 BBs at least in those pots and get shown Top pair too often.

How do you decide which line to take?
When will you be able to lay this down?

If you start calling they bet 2pair to the river so it seems you gotta decide what to do on flop. Fold or take it to showdown. It costs at least 2BBs to take it to showdown and the pot is like 7BB on showdown so u gotta win at least 30% of the times.

Any insight in this common hardplayed scenario is welcomed.
Any links to good discussions is appreciated(I suck at searching).