LOL - I think it's time for you to get a new scale!
Seriously, it really sounds to me like your scale isn't working. And if your scale doesn't work, how do you know if you've lost or gained weight? I had similar experiences with my scale--I could step on it, step off, then step on again and get a completely different reading. But all the mysterious weight flunctuations stopped as soon as I bought a new one. You can probably get a good scale (digital, even) for US $20 or $30--make the investment, no matter how often you weight yourself, you have to have a reliable scale!