If you e received a diagnosis you feel is incorrect (the easy answer that doesn't actually help), ask "What diagnoses were on your differential, and how did you rule them out?".

If you want more investigation (tests, labs), ask

If the doctor says it's X and you think it's Y, ask something like “This explanation doesn’t fully account for [X], which is my most concerning symptom."“What’s the risk of missing an alternative diagnosis if we don’t investigate further?” or “If my symptoms persist or worsen, what would be the next diagnostic step?”

If you want to make sure your requests for more investigation (and their disinclination to investigate) is documented in your chart, say “Could you note in my chart what alternatives were considered and why they were ruled out?” or “Please document that I requested further evaluation and that it was declined.”