Being able to hear chord changes is a skill that can be developed with practice.
Here is how to practice it.
Below is a list of 2-chord songs that use the chord pairs you're practicing with.
Choose songs you know well and try to figure out where the chords change by yourself just from a memory of how the song goes. Strum along on your instrument and see if you can work the song out using your favorite pair of chords. You might surprise yourself.
Then listen to the songs on a CD and see if you can hear the chord changes. Some arrangements may include more chords so don’t get too frustrated. At this point, it’s more important to learn to play songs than to learn to hear them off recordings.
The hearing of songs is a skill that will quickly get better the more you play songs.
Chicken Reel (the Foghorn Leghorn cartoon theme song)
Clementine (This in 3/4 waltz time which requires different strumming patterns)
Hot Corn, Cold Corn
How Would You Like?
Rock-a My Soul
Take Me Back to Tulsa
Try any other two-chord songs that you can figure out. See if the singing is better or worse in this new key. It may be better on some songs and worse on others!?!