First off, you've lost a whole pants size!! That's excellent!!
In my opinion,
that's the kind of measurement that means the most.
As for the scale, I agree 100% that you need to pick one and stick with it. EVEN if that scale is off/different than others you've tried, it will still show you your total loss of pounds. You could start fresh tomorrow and consider your weight on the scale in the morning to be your new starting weight, and then gauge your weight loss based on that number.
I -- like an idiot -- broke my own "one scale only" rule yesterday. Again. On the stupid DOG scale at work, which consistently tells me I'm 10 lbs heavier than my scale at home says. Of course, in the case of that scale it's calibrated to have something lying on it, not standing. But the point is, I KNOW I didn't gain 10 lbs in the space of 3 hours, so I grumbled, laughed, and swore I'd never use the stupid thing again.