「何でそんな遠い所まで行くの?(通うの?)」は、
①Why do you go to ~ that far way?
②What makes you visit ~ that far away?
などでどうでしょうか?^^
※~に行先の場所を入れます。
「皮膚科医」だと dermatologist なので、
①Why do you go to the dermatologist that far way?
②What makes you visit the dermatologist that far away?
ですね^^