What is the ruling on blood that came down two days after ghusl from menstruation, then stopped, and returned on the fourteenth day? Is it considered menstruation or istihadah, and does the regular cycle change due to breastfeeding?

If the total number of days of bleeding and purity during it exceeds fifteen days, then the woman is in a state of istihadah (non-menstrual vaginal bleeding). The menses from this period is what corresponds to her regular habit, and anything else is istihadah. If the woman does not have a regular habit, then she acts according to sound discrimination (of blood types), otherwise, she counts six or seven days of the month as menses, and anything beyond that is istihadah. The habit may change due to breastfeeding or other reasons.