This question had been asked at least a couple times, and the answer is always the same, along the lines of
startActivity(new Intent(Intent.ACTION_VIEW, Uri.parse("market://details?id=" + getPackageName())));
The problem is, it doesn't work for me. It opens the main Google Play page, not my app's page. My app is indeed on Google Play, had been for 4 years. Interestingly, this code did work a couple years ago when I first written it but now it doesn't.