This matter also bothers me. If the blinds are low I call/play almost all the small pairs , if raised a little I also call , if raised big by one I fold .
If I don't hit sth on flop I fold , I don't expect anything on the turn .
On bigger blind levels I play only big pairs if I have the chance and the higher the blinds are the higher pocket pairs and the more in position I play .
If one pocket pair is overpair , I don't trust playing it , I just check it , at least if I don't have need of more chips/blinds . If many villains have called a raise/reraise and the pot is big enough giving me the odds to play a PP sacrificing a lot of my chips , well I don't know when this is right or not exactly mathematically , so I don't do it YET , I'm still studying it .
But I must say when it comes to PP I prefer applying the 2to10 rule , at least by now I haven't faced a problem concerning playing PP , this rule is very reliable