Just had my 1 month check up and only lost 4 lbs!

Even my nurse said that's "quite low". She did say it's not unheard of...she's seen slow starters but eventually the weight loss suddenly kicks in and they catch up pretty quickly. Still, I am discouraged and want to do everything I can to maximize my results. I have followed the diet exactly, so I know it isn't overeating or eating the wrong things. Looking back through my log - I do realize that there are a few days I didn't get my 64oz water. I wonder if I could be mildly dehydrated and retaining water and/or slowing my fat burning? My plan is to really focus on the liquids and make sure I get the required amount for the next couple weeks and see if the scale starts moving.
The other thing that occurs to me is that my PCP has told me in the past that my thyroid was "a little low", and when I had my pre-surgery blood work - it came back a bit low again. The PCP decided to keep an eye on it, but I've not been medicated or referred to a specialist to date. Maybe the low thyroid is causing an issue?
Anyone had any experience with lower than usual weight loss this soon after surgery? How did you get over the hump?