Based on Holy Power Notifier by gilbertsmith123
This modified version version of Holy Power will show you when you have 3 and 5 Holy Power.
When you have 3, a yellow icon will appear over your head, when you have 5, the icon will turn red.
The original addon used to count each holy power, but as I maintained the addon for myself over the years, I only ever used the notifications at 3 and 5.