Gi doc and pooping issues!

My little one is going to a GI doctor this week due to pooping issues she's been having.

She screams for like 30 minutes Everytime she has to poop, it's either hard or water there is no in-between, and its either grey or has a greyish tint to it everytime.

Anyone have experience with these type of issues that could possibly tell me what to expect at the doctor this week or what the cause was for your little?

I'm very nervous and would just like some idea of what to expect