No worries. I'm a big girl, too (230#, 5'7"). Lost 15#+ in the first 16 weeks or so. Then I started putting it back. From 20-26 weeks I gained 5.5#, but was just in again last Friday at 29w and weighed exactly the same as at 26w. Midwife said not to worry a bit. At 30 weeks, I'm pre-preg weight.
I think what's happening is that I'm just plain old eating better. I actually feel thinner when I put my hands on my hips, and in my face. So, I think I'm just converting extra 'me' weight to baby weight and not having a net gain.
I think if i was still losing weight, they'd be keeping a closer eye on me.