congratulations for admitting your problem and being willing to seek help. the best thing to do right now is tell your mother about your eating disorder and ask her to take you to a doctor or psychologist who can help you. try to explain to her that you're not crazy, and try to tell her why you feel the way you do about food and how she can help you. tell her how important it is that she support you and try to understand your disorder. if necessary, give her a few books or websites that explain eating disorders properly.
your next step is to get yourself to your doctor and get a recommendation for a psychologist, eating disorder specialist and nutritionist. be prepared to answer a lot of questions honestly about yourself, your eating disorder and pretty much anything that could relate to your eating habits.
start to increase your calories slowly. try adding about two hundred calories per day, so that you gradually become accustomed to eating more. the same thing could be done for drinking liquids. at first, only a little bit, then a little more the next day, until you feel comfortable drinking normal amounts.
dehydration can be really serious and can mess up your electrolytes and cause tons of other health problems. you may gain a little (no more than two or three pounds) when you start drinking again, but it's all water weight. none of it is fat, it's just the water your body needs. it will not be permanently stuck there, and if you were to stop drinking liquids again, it would go away within about two days.
also, try to weigh yourself only once per day so that you don't become even more paranoid and freaked out by the number on the scale. i know that's really difficult. i used to weigh myself all the time, too, until i was forced not to know my weight for three weeks while i was in the hospital, and now i just weigh myself once per week. it would probably be best to start just weighing yourself in the morning, because that's when your weight is most accurate.
good luck with your recovery. as someone who is currently in recovery for an eating disorder, i can tell you that it's a very difficult thing to go through, but keep your goal of recovery in mind and things will get easier. if you have any more questions at all, or need someone to discuss recovery with, you can email me at firstname.lastname@example.org