The doctor's office is generally thought to be the whole area: waiting room, receptionist's area, examining room, and his personal office. Often we say, "I have to go to the doctor's" and don't even finish the sentence. Or we could say, "I have to go to the doctor."
I have certainly heard it said (in the past tense) "...when I was in the doctor's office..." and I suspect the person never was really in anyone's office.
But you are right, the doctor's office should just be that little room with his desk.
The place you have to pull your shirt up or step on the scale is usually called the examining room or examination room.
I only speak for North America. And then, only for the tiny part of it that I have lived in.
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