I just wanted to emphasize this point. Once hair loss start, it is hair that went into the "sleep" cycle, sometime back, most likely around the time of WLS. Once the folicle "wakes up", it pushes the old hair out, and that's your hair loss. Most of the time hair loss doesn't begin until 2-3 months out from surgery.
I also wanted to note that you could be doing everything right, hitting your protein, taking biotin from the beginning and still have hair loss. I think there is some genetics or luck involved as well.