بسم الله الرحمن الرحيم
There is rule regarding menses that if a woman has a habit i.e. she bleeds for fixed days like 4 or 5 days, then if she sees blood after that, then if it continues within 10 days then all ten days will be considered as menses. But if it continues more than 10 days, then only the days of regular habit (e.g. 4 or 5 days) will be considered menses and the rest will be treated as istihaza (non-menstrual bleeding). If you have a habit of four or five days, then start salah, sawm, tilawat etc after the bleedings stops performing ghusl. If the bleeding starts after seventh day, then all the salah offered during these days will rendered as invalid but you will be asked to reoffer them, but you will have to make qadha of all missed fasts. If the bleeding did not start again within ten days then all salah offered during these days will be valid and you will not have to make qadha of fasts kept in those days. If the bleeding starts again after 10 days, then it will be considered non-menstrual bleeding which will not prevent salah and fast.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.