When do I see which doctor I am assigned too?

This will be my first visit to mayo in Minn. I went for years to Floridas mayo. I always knew who I was seeing and that info was also in my patient portal ahead of time. Thsi time, they have not yet assigned my doctor to me. It will be a gastro visit. Upon calling they said it depends which gastro is there that day and available so I will not know ahead of time!?!? This concerns me because I am unsure it will even end up being a doctor. Let alone not haveing any idea who they are or looking them up ahead of time. I have a serioulsy rare disease. I get dimissed a lot so I always like to know who I will be dealing with. I find it strange that you walk in with zero idea who you will be seeing. It is not on my portal nor can they tell me when I call. Is this normal???