All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are not obliged to inform your fiancé now about your need to use contraceptive pills, but if Allaah predestines that you marry at a time when getting pregnant would be harmful to the fetus, then you may inform your husband about your case so that he would allow you to use this medicine.
However, after contracting your marriage with your fiancé you may agree with the doctor who treats you to write a report for you in his presence stating that you are in need of these pills. Indeed, this is better so that he would accept and understand the matter and this is what is expected from him, Allaah willing.
Allaah Knows best.