Write your questions down now
Open your notes app and start a running list. Every time you think 'I should ask about that,' add it. You will blank the second you walk into the office.
Bring your partner if you can
Two sets of ears are better than one when you're running on 4 hours of sleep. One of you can hold the baby while the other takes notes.
Don't compare to the other babies in the waiting room
Every baby in that room is on their own curve. The 3-week-old who seems twice the size of yours might have been born 3 pounds heavier. It means nothing.
Ask 'what should I watch for before the next visit?'
This one question reduces so much anxiety between appointments. You'll know what's normal and what actually warrants a call.
Mention how you're feeling too
Your pediatrician can screen for postpartum depression and connect you with resources. They care about the parent, not just the baby.