Just talked to my new oncologist today about this as I am 47 have just finished chemo, my periods have stopped and I am going through those wonderful hot flushes and night sweats and am not getting much sleep. He said given my age I had a 90% chance of the chemopause/menopause I am experiencing being permanent but there is still a chance my periods could come back anytime in the next 2 years and be very short cycle (like you describe) and/or irregular. This is because the chemo actually damages the ovarian tissue and oestrogen production so everything gets mucked up. They can tell from a blood test whether someone is in menopause or peri menopause (such prior to menopause) but the test won't tell you how long it will last symptoms or periods will last. Maybe gynaecologist can manage symptoms better? Ablation may be an option???
Hope you get relief soon