It’s because oestrogen is stored in your fat. As you loose weight the oestrogen is released into your bloodstream giving you a hormonal flush. Heavier/lighter, more/less frequent cycles, increased or decreased PMT symptoms, etc. plus the stress of the surgery & changed diet add to it all. I was menopausal when I had the surgery & all my hot flushes disappeared. They all can back though once I’d lost a lot of my weight ☹️. Your cycles will settle again too.
PS - you can also become more fertile. Many surgeons suggest doubling up on contraceptives.
Someone I know had sleeve surgery and she had the same issue. Basically her period never stopped. She had it for like 2 months and then I think they gave her some meds or something to address it. I really don't know the details but I know she got it resolved.
