Is it obligatory to make up past prayers and fasts due to not performing proper ghusl (ritual bath) after menstruation in youth, and is expiation required for the days whose number is unknown?

If you immerse your body in water with the intention of performing ghusl (ritual purification) from menstruation, then your ghusl is valid, and your prayer after it is valid. Ghusl is not a condition for the validity of fasting after purification from menstruation, unlike prayer, circumambulation (tawaf), recitation of the Quran, and carrying the mushaf (copy of the Quran), which are not permissible until after ghusl. It is advised not to pay attention to obsessive whispers regarding purity.