you're in the infamous three-week stall. Happens to most of us. It's not ALWAYS the third week, but that's the most common (hence, the name), but most of us experience our first major stall within the first month or so after surgery. Best way to deal with it is to make sure you're following your clinic's plan to a "T", and stay off the scale for a few days. As long as you're following your program, the stall WILL break, and you'll be on your way again. It usually takes 1-3 weeks. It's basically your system recalibrating - and this will likely be the first of many stalls.
re: bowel movements - constipation is a common issue after WLS. It's because of the high protein diet and supplements some of us take (iron and calcium are particularly notorious for this). It should improve once you start eating fiber again, but many of us have to take things like Miralax, magnesium tablets, or stool softeners daily to keep on top of it.