I generally do step tapes 5 or 6 days/week and have no problems with my feet or knees. However, I am now on vacation in the US for over 2 months and have been doing a lot of walking to keep in shape. Although I am using good shoes, my feet are real sore and achy. What am I doing wrong? I don't normally walk for fitness at home, so is it just that my feet need time to adjust to the new activity??