Yeah, that is annoying. I'm not sure what the exact math the site uses, but it seems like it only makes an estimation of your loss/gain per week based on your most recent weigh in... not on the actual amount you've lost/gained during a week. Although I sort of understand the logic of it (if you kept on losing at this rate you'd lose X amount in a week's time), it can be discouraging if you've generally lost weight over the past week and all you see is "steady" or "gaining" because of your most recent weigh in. It's also not so good if you lose a pound and it says you'll be "losing 3.8 pounds per week" or something like that, because if it's not realistic then people can get discouraged.
Anyway, blah blah blah. :) Just to say I hear your pain... it's a part of the website's system, not anything to do with your actual weight. You're doing a good job!