the issue with your weight at the doctor's office is that you have more variables. in other words, the closest you'll get to what you actually weigh is by weighing first thing in the morning, after going to the bathroom but before you ingest anything. most people, by the time they get to the doctor's office, have had food and beverages, which doesn't sound like much, but water is darn heavy [half a pound per cup heavy]. so if you drink a cup of water and a cup of coffee before making it to the doc's, there is a pound right there. and if you drink more, you weigh more. eventually as your body processes the things you ingest they are converted to energy and used or waste and then passed, but until you hit that point, you may as well stand on the scale with the things you eat. and what you eat has an effect on how much water your retain. and what exercises or other basic things you do have an effect on how much water you retain. because your body needs a lot of water, it keeps a pretty decent store on hand because it uses water in so many different basic repairs on your body as well as basic functions. and more water means a higher number on the scale, though it has to do more with what your body is processing rather than your actual weight.
-google first. ask questions later.