Do I need to tell you about my previous sick leave when I apply for a job?

No, you are not obliged to inform your new employer about previous sick leave, either in an application or during an interview.
However, you should prepare to answer this question during the interview, as the employer may ask about periods of interruption in your work experience. Have an answer that you feel comfortable saying without getting defensive or making excuses. Focus on what you have learned about yourself during this time and that you are now focused on the future.