Gaining 6 to 10 pounds in 11 days is almost never all muscle or fat. Most of that early increase is likely just water, glycogen, or having more food and water in your body. Testosterone can make your body hold onto more water, especially at first. Changes in your carb or salt intake while traveling can also make the scale jump. Being one pound heavier after walking 25,000 steps does not mean much, since your weight can fluctuate by several pounds from day to day. Try not to stress about single weigh-ins. Instead, weigh yourself each morning under the same conditions and look at your weekly averages. In another three or four weeks, you will have a much clearer picture of your real progress.