No weight gain

Pr

So I finally brought it up to my dr, my pre pregnancy weight is 170.6, my weight has stayed the same up until July 11th, it went up to 171.0, I had another appointment July 25th & it went back down to 170.6, now today again it’s 170.6 & I was so sure it was gonna be at least 174+ my belly is measuring fine but it’s just odd I’m in my third trimester & have gained nothing. She’s scheduled a growth ultrasound, she mentioned something about me having too much fluid. Idk what that means but I’m kinda worried.. lol has anyone else not gained any weight at all, obviously I’m not super thin, there’s plenty room for baby but won’t his weight gain reflect mine??