By the way, we would never say “At the Doctor”. It’s always “At the Doctor‘s”. This is short for “At the Doctor’s surgery”, although this expanded form is rarely said. So we would say “I’m going to the Doctor’s”, “I’m at the Doctor’s”, and so on. We can, however, use “Doctor” without the possessive with the statement “I’m going to see the Doctor”. Also, it’s worth mentioning that a surgery, in this context, is more-or-less an office and not anything like an operating theatre.