Hi Carly and welcome to the board!
Congratulations on your decision to lose weight, I hope things go well for you. I thought I'd post in response to your concerns about coffee, as I'm a massive coffee fan too. I must admit that I don't drink anywhere near 20 cups a day, but I could never give it up completely!
Coffee itself has very few, if any, calories. The problem is that we tend to add things to it, which in turn adds extra calories. If you drink black coffee and just add a sweetner, you will find that you are drinking something which is virtually calorie free. If you don't like the idea of sweetners, perhaps you could try stevia, a natural sweetner instead.
If you like to drink your coffee with milk, I don't see the harm in having 2-3 cups a day, with just a splash of low fat/no fat/light milk. I drink 2 skinny lattes every day and it's never affected my ability to lose weight. I would suggest going to www.calorieking.com.au
, which is a great site for working out what your calorie intake should be. It's free, you simply submit your height, age and weight and it works it out for you. There is also a huge food database there, so you can look up the calorie content of common foods and work out if you're eating too much throughout the day. If you do this, you should be able to work out a way to incorporate your 2-3 coffees a day into your calorie allowance.
Another suggestion would be to try the nescafe latte sachets that you can get from any supermarket. You can get flavours like mocha, skinny latte and cappucino, which are 99% fat free and only have about 40 calories per serve. You just make these by adding water, so you save calories from not adding milk. (To be honest, I DO like to add a splash of milk to mine, and sometimes an extra teaspoon of coffee to give it a bit more of a kick!)
In relation to why you're feeling so tired all of the time, it might be because you need to work on your eating habits a little. We get our energy from the foods we consume, so if you regularly skip meals and just drink coffee instead, your body has very little to 'fuel' itself with. This could be why you often feel so tired. I would suggest eating low GI (glycemic index) foods, which will help you feel full for longer and give you a constant supply of energy between meals.
All the best with your weightloss plans, keep us posted and shout out if you need anything