Currently experiencing the same thing. I hear this is very common at the time. My doctor advised I up my activity (I'm only clear to walk until week 6) and increase water intake, but that this stall is normal. Weight gain could potentially be bloating, water, hormones, a whole slew of things.
As someone who militantly believed in CICO and that hormones were a cop out, this has been a tough pill to swallow but following my doctors advice has been yielding more results than my previous beliefs and efforts.