Forgive the format, but the hand is from a site where I can't (or can't figure out how to) download the history, so the action and bet amounts are from memory. BB just sat in, and the CO hasn't done anything particularly remarkable in the hour or so I've been at the table with him, so no reads. All stacks are approximately $25. I'm in MP with A

A
Hero opens for $1, CO calls, BB calls. Pot is $3.10.
Flop is K

5

4
BB checks, hero bets $2, CO calls, BB calls. Pot is $13.10.
Turn is 10
BB checks, hero bets $9, CO raises to $16, BB calls, hero...?
I have been trying to improve my bet sizing, but the presence of the tagalong BB, as well as having one villain in front and one behind made this whole hand just feel awkward. How do you guys play it all the way through?