How often do you weigh yourself?
I have a 10 pound weight that I put on my scale to record for accuracy before I ever step on. After I check the scale I get naked and step on!!! If you have a weight, try checking your scale. Maybe you did lose 9 pounds!!! Or maybe the ground was unlevel, or maybe your scale was having a bad day!
It never hurts to check it before spending money on another one when it might just be ok