What is the ruling concerning blood that appeared a few days before the expected time of menstruation, and continued to flow along with the menstrual blood that immediately followed the first blood, knowing that the first blood flow lasted for 11 days, and the second blood appeared on the 12th day and has continued for 7 days and is still ongoing, and knowing that the first blood was light and transparent, and the second was heavy and dark in color? Should I fast with the appearance of this blood, considering it istihadah (non-menstrual vaginal bleeding), or should I break my fast?

If the bleeding is continuous as you described, then you are experiencing istihaadah (non-menstrual vaginal bleeding), and you must refer to your previous regular period. The first eight days are menstruation, and anything beyond that is istihaadah.

Perform ghusl (ritual bath) after your menstrual days end, and then pray and fast. You will have the rulings applicable to ritually pure women.

Make up all the days you missed fasting, whether they were due to menstruation or istihaadah, and also the prayers you missed thinking you were menstruating.

A layperson imitates whomever they trust among the people of knowledge for their knowledge and piety.