1. You shouldn't go from normal eating to fasting - its stressful on your system, leaves lots of gunk in your digestive tract for a long period of time, and makes it extremely difficult to get through the fast psychologically and physically.
Instead you should be on a pre-fast diet, ideally vegan for months and raw fruits and vegetables in decreasing quantities for the week proceeding the fast - but since thats not possible given your goals, at least raw vegetables and fruit in decreasing quantities for a week or at least five days or at the very least a few days to clean out your system.
2. Use water only - not fruit juice, not diet soda - fruit juice keeps you in a glucose based rather than fatty acid/ketone based metabolism (ketosis) which would lead to muscle wasting, slower weight loss and difficulty fasting. Diet soda contains some carbs (just too few, i.e. less than 5 calories per serving, to be required to be listed by the FDA which allows items with less than 5 calories per serving to be misleadingly advertised as calorie free even when everyone consumes more than one serving). More importantly the sweetness and the artificial sweeteners lead to food cravings which makes a fast much more psychologically demanding.
3. If you live with your family and they question it, be absolutely firm and resolute, explain your reasons for it, and explain why this is emotionally, socially, and health wise an important and correct decision for you. *EDUCATE YOURSELF* and become an expert on fasting both for your own benefit (and safety) and
4. Breaking the fast properly is absolutely vital. An improperly broken fast can lead to refeeding syndrome, a potentially fatal condition. You need to be consuming phoshorus, magnesium, and potassium after a fast in proportion to the amount of carbs you consume in order to prevent refeeding syndrome (which is occurs in people depleted of those three nutrients, like fasters, when they eat carbs without replacing those nutrients). Breaking it on meat or bread for example could be dangerous.
5. If you want to keep your weight off, you absolutely cannot go back to the way you were eating before ever or you'll get it back. More than that however, even a standard *HEALTHY* low calorie diet that most dieters use to lose weight will lead to weight gain in someone who has just fasted, because fasting will slow your metabolism for at least a month and probably longer (but not in the long term unless you did it improperly and lost muscle). You need to ignore all the standard guidelines for dieters - 1200 calories a day is probably too much for you after fasting if you want to keep the weight off. Think less than 800. You also need to eat an extremely healthy way - i.e. low fat vegan and mostly vegetables. In any case a very low calorie diet is likely unsustainable for even short periods of time unless you are eating a nutrient rich diet, one composed primarily of non-starchy low fat vegetables (kale, mustard greens, spinach, dark lettuce etc have among the best nutrient to calorie ratios). This will allow you to feel full with less since non-starchy vegetables are satisfying and have a good glycemic index, not appetite stimulating like the foods most American eat.
6. Don't over do it on water - drink according to thirst. Downing a gallon within a couple of hours can lead to water intoxication, which is potentially fatal.
7. 22 lbs in 16 days is *possible* especially if you're obese or retaining an unusual amount of fluids at the start of your fast or you do heavy exercise (a bad idea since it risks messing up your electrolyte balance and consumes more energy than your fat can supply - the remainder of which comes mostly from muscle). However it is unlikely - while you will possibly lose weight rapidly at the beginning of a fast, other days you'll see little or no change on the scale (this is because of different levels of water and waste retention). On average people lose about a pound a day averaged over the course of the fast. This is still faster weight loss than virtually anything else you can do, but its probably not 22 lbs in 16 days. It is best not to set goals in terms of weight loss because its out of your control - you are losing weight as fast as you realistically can on a fast (certainly way faster than any diet). If you aren't satisfied with your weight loss you can always extend it an extra few days.
8. There are often emotional and physical highs and lows. You will likely feel sick and tired your first three or four days (after which you will feel much better but probably still easily fatigued - which is alright you should be resting - do not engage in manual labor). For a fast to be successful you need to have confidence that these will pass. And they will. I have been fasting for 23 days as of today - I have had episodes of extreme fatigue and stomach pain - but they passed. It is best to keep in mind why you're doing what you're doing. Only fast if you can be committed and confident in yourself.
9. At the end, you will look and feel so much better than you did before and you'll know that you can truly do without food - food is always optional (except after say 60 days). You can feel better about yourself instead of relying on food to give you emotional relief and comfort. You have control over what you eat - you don't have to eat 'the whole thing' of anything. You do not need much food - you can be fine with small portions. The overwhelming majority of people, fat or thin, eat for pleasure not for nutrition even when they believe they are making healthy choices - and this is the road to either obesity or torment. But once you've fasted successfully, you know you don't have to.