。
You're acting so weird — go get your head examined.
Literal
Weird things [object-を] do because head [object-を] examine receive [polite imperative-なさい] [assertion-よ].
変なことをするから sets up the reason: 'because you do weird things.' 頭を診てもらいなさい combines 診てもらう (receive the favor of being examined) with the polite imperative なさい. The overall tone is scolding but caring — likely from a parent or close friend. よ at the end underlines the point.