Depending on your reasons for changing your lifestyle, whether you are trying to increase your fitness level or you are trying to lose weight; you have to be realistic with yourself.
Contrary to the magazines in the racks next to the checkout at the grocery store, it is not realistic (or sustainable) to lose 10 pounds in 10 days – or whatever the flavor of the day is. A rule of thumb: if it sounds too good to be true, it is.
Safe, sustainable weight loss will generally be around 2 lbs per week. It seems unbearably slow, and you need to make long term changes to get long term results. The up side is that you will be far more likely to keep the weight off after you have reached your target.
Similarily, it’s not realistic to go from a sedentary lifestyle to expecting to run a marathon in only a few months. You need to give yourself time to improve your overall fitness level, and make sure you’re exercising safely to avoid injury. The last thing you need is to lose all (or some) of the work you’ve put in to your personal fitness because you have to recover from an injury.
Moral of the story: Be realistic, be patient.