How to stop positive lookbehind from going too far behind

Expression:

(?<=d)(.*?)(?=but) 

catches:

og1 dog2 

from string:

"adog1 dog2 but"

What changes should I make make to the expression to catch only

og2 

You could use this regex:

(?<=d)([^d]*)(?=but)

The change I have made is the middle component:

([^d]*)

This ensures that we don't cross another letter d before asserting that but follows. This means that the match will be the last d before but.

Demo