Sudden weight loss?

Anyone else started losing weight around 26/27 weeks?  I was up to about 18.5 pounds gained and am now down to 16 pounds gained in about a week.  I know it could be water weight, but I haven't changed my diet / exercise and weigh myself daily, so I know it's not a fluke reading.  I've been pretty consistent in weight gain throughout the 2nd trimester (1 pound/week).  Going to ask my doctor at my next appointment, but thought I'd see if anyone else has had this experience.