How long before you can reasonably say something is or is not doing anything?

Following this because I am in the same place and have no idea what to ask at the appointment.

Is it normal to feel worse before better? Nobody told me that.

Is a baseline blood test really necessary before starting something like this?

Stupid question: how do you know whether what is in the vial matches the label at all?

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