Photograph everything before you open it. Ten seconds, settles most disputes. Same for me with Australia Post, unfortunately.

Changing prescriber does not reset anything, and people discover that the hard way.

Sorry for the basic question, but how do you actually start one of these diaries?

Bring a list. Embarrassment makes everyone forget things, including you.

You are not imagining it and you are not being difficult. Document it and take the document in.