yes - it's related to the surgery. It affects your hormones. A lot of women experience screwed up menstrual cycles (and/or have weird moods) for the first few weeks or months after surgery. Estrogen is stored in fat cells, and the theory I've read is that it's released during rapid weight loss (don't know if the latter part of that is true, but it IS stored in fat cells, and lots of women DO have hormonal issues after surgery because of it). It'll eventually stabilize and things will be back to normal.
I don't know the answer to your second question, though.