I have severe menorrhagia for the past 18 months. Please suggest an effective way to get cured.

Hi doctor,

I have severe menorrhagia for the past 18 months, were two of my periods have lasted 48 to 50 days of bleeding. I visited the GP countless times, who tried changing my prescription of contraceptives, put me on Norethisterone, had scans done and blood tests. I changed from Levlen to Diane, and they said it was caused by endocrine dysfunction, which was approached by changing my dose of thyroxine. However, my period is still going for more than two weeks, and I am really concerned that there is still an issue to address that has not been discovered yet. I had issues with this since mid-last year may be relevant, congenital hypothyroidism. The previous history of the same issue, I had a 48 day and 50 day period investigated since last year. I am taking Diane Levothyroxine (100,150 mg alternating daily) took Norethisterone, which did not help the issue. I got an ultrasound to test to check for growths or polyps. Kindly help me.