Maybe you could ask for a plan of how the rewards work within your care plan?
It seems a bit harsh if you are doing your bit (- and you have done really well since the nurse upset you so much -) so having a clear idea of what you can 'expect' might motivate you to keep going on so well. It all sounds a bit random - and I wonder if it might be to do with staffing? But when you are trying to keep the lid on it all you should be entitled to know your 'rights' for doing that. If you are starting to feel 'cheated' by not getting any rewards/privileges that could make you lose it big time. Nobody wants that - especially me!
Not sure I've said that very well but I hope you know what I mean - yes?
Hope your brain can switch off tonight and you get some sleep.