Does divorce occur with the words "Rejoice, it's over, but after the exams," with the intention of divorce? And is the last divorce final and irrevocable if one is certain of the occurrence of the first divorce but doubts the second?

What was issued from you is merely a promise to divorce, by which no divorce occurs, and you are not obligated to fulfill it. Sheikh al-Islam Ibn Taymiyyah said: "A promise to divorce does not constitute divorce, even if its wordings are numerous, nor is it obligatory or even recommended to fulfill this promise." You must be patient with your wife and strive to reform her.