What made you laugh in the doctor's waiting room? (4,6)

'waiting room?' is the definition.
I know nothing about this answer so I can't tell whether this works.

'what made you laugh in the doctor's' is the wordplay.
I cannot quite understand how this works, but
'you' could be 'u' (homophones) and 'u' is located in the answer.
'doctor' could be 'mo' (medical officer) and 'mo' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?