I noticed that when I get on my scale I see one weight and I say that can't be right. So after I check my weight again it gives me a whole new number. Then again it another number. Each time I stand perfectly still and it's on a flat surface. I can't even tell what my weight is anymore
How much is it changing? .2? .4? If so, it's HOW you are positioned on the scale - more weight forward, or backwards. Remember, even on a doctors scale, it wavers as it tries to balance... same with a digital scale and I think it "calls it" when sometimes it's not yet settled on a precise number, but it's usually on in tenths of a pound.
+1 on the suggestion to replace the battery and, if that doesn't work, the scale. A well-functioning digital scale may fluctuate +/- 0.4 (or 0.5, if your scale only measures in half-pound increments), but it shouldn't fluctuate by 4-5 pounds.