Just wanted to say that sounds very much what happened to me in the last year or so, I would alternate weeks and weeks without a period with occasional sixteen day 'perma-periods' followed by random spotting - no fun! So disconcerting, but quite normal. At one point the periods stopped altogether, I had a blood test (I know they aren't advised, but I was curious!) and it said I was firmly postmenopausal. Two months went by, and then... six more absolutely regular periods until a scanty last one. No rhyme or reason at all.