Hi, I had a vsg on 28th Feb 2017. My bmi was about 53 at it's highest, and it's now about 41. I also have autoimmune hypothyroid and PCOS, and I was also worried that I would loose weight even with the vsg. But I am! After the initial quick weighloss over the first few weeks my loss has slowed down to about 1-3lb per week, which is on the slower side. However I'm really happy with my progress and just happy to see the weight dropping off. Plus I think slower weight loss is healthier and better in reducing loose skin, so I'm actually pleased it's a bit slower.
In regards to my PCOS, I had a period fairly soon after starting my pre-op diet (first in about 100 days!), then had another one 26 days later! For a fleeting moment I thought the surgery might have cured my PCOS (as I've heard it can instantly cure diabetes), however I'm now on about day 60 of this current cycle, so no instant cure, but I'm sure the weight loss will help.
good luck with your surgery, I'm so so happy I went through with mine.