The conditions that could be causing this depend on your age. If you are post-menopausal and have stopped having regular periods, you need to see an obstetrician as soon as possible. Abnormal menstrual bleeding
in a post-menopausal woman can be caused by benign conditions such as fibroids, but is concerning for endometrial cancer and requires a pelvic ultrasound
or endometrial biopsy to be ruled out. If you are pre-menopausal but not having menstrual periods and now having irregular cycles there are other possible processes underlying this change. You may have lost more weight than is healthy and that is causing you to have irregular periods. You could have changes in your hormone levels, including your thyroid hormone or your sex hormones (FSH, LH and estrogen); if you are premenopausal you could be going into menopause which could be causing irregular periods. It sounds like you've already had some testing done. I would recommend seeing your doctor
to discuss your symptoms and your concerns, to discuss what the tests that have already been done have shown, and how best to proceed; your doctor will know your age and medical history and can do a good physical exam.