Only 医者 is correct. You NEVER refer to yourself as ～さん！ You only use ～さん when referring to people OTHER than yourself. As for 先生：　先生 is not a person, it is a TITLE, like Mr. Mrs, Dr, Professor, etc. The correct way to call yourself a teacher is: 私は教師です。 If you want to say that Mr. Suzuki is a teacher, you say: 鈴木先生も教師です。 Suzuki gets the 先生 title, because he is a teacher. You don't call him 鈴木さん。 Doctors and masters of martial arts also get the title 先生. What a language!