بسم الله الرحمن الرحيم
(Fatwa: 83/82/N=01/1435)
(1) If you had a fixed habit, but due to some illness your period prolonged to more than 10 days then in this case in each month after the menses starts your habit shall be counted as your period in which your salah shall be exempted and rest of the days shall be counted as istihaza in which you will do ghusl once and start offering salah. But if you are experiencing this from the time you turned adult or you had a habit of total ten days then each month from the starting of the blood you shall count ten days as menses and rest ones as istihaza. It is so mentioned in the most of the books of fiqh.
(2) Recite Ya Salam 142 times daily after Fajr and Maghrib salah and during your period without salah. In-shaAllah, soon your problem shall be removed. May Allah grant you health! May Allah bless you good and pious children! Amen!
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband