I have alot of trouble catching the chord changes too - especially when the song takes you out of the G, C and D. If you can see the lead player's hands, sometimes you can see him make the change. I also try to listen to it once with my eyes closed. I also try to find the pattern. There also seems to be a general pattern that many of the songs we're playing follow: like in G it seems like alot of songs go from the 1 (G) to the 3 (C chord) and stay there for two measures, then return to the 1 (G) then to the 5 (D). But usually, the change to the 5 is only for a single measure and you don't hang there before returning to the 1.
If the song leaves that general pattern, I'm as lost as you are !!!