It may be because of problems in weight, hormone,
thyroid, uterus etc. Consult gynaecologist. Please read https://drsujoydasgupta.continuouscare.io/post/8-ways-to-avoid-irregular-menstruation/2339
Health Tips
https://drsujoydasgupta.continuouscare.io/post/8-ways-to-avoid-irregular-menstruation/2339