1.You probably spend a lot of time trying to make your mother feel upbeat and good. You should do that if she's feeling particularly down or afraid. But in general, I think you should just be yourself.
Your mother is suffering from a deadly disease. She knows what the consequences might be. She also knows that you're terribly scared, because she knows how much you love her.
It is only natural to be afraid. So accept it. The people who have seen their parents suffer from cancer unanimously say that it is better to be your natural self. If at some points you find some hope, you'll certainly tell her so, and will try to cheer her up for that, like you're doing. But don't make her feel something that you don't feel. I mean, do not pretend and do not give her any false hope. This will make you feel exactly as you're feeling now-empty and devoid of energy.
2. Talk to her like you'd talk to her under ordinary circumstances, I mean forgetting, for those particular minutes/hours that you spend talking to each other, that she has cancer. Talk to her as any daughter talks to her mother.
3. Make sure you let her know HOW MUCH YOU LOVE HER. Do as much as you can for her. Spend as much time as you can, together.
4. Find out what are the things she likes or wants. Try to fulfill as many of her wishes or longings as you can. This will give you a deep sense of satisfaction and fulfillment.
5. When a woman is ill like that, usually the biggest worry for her is the safety and wellbeing of her children. So let her know you're alright, you're strong and you're capable of taking care of yourself.
6. Another very important thing that you can do is finding a community of people who are like you. You can do this by googling cancer support group', and then finding one in your locality. If you can find one that is suitable for you, you'll get the answers to many of your questions simultaneously. First of all, you'll meet people who have gone through situations which are either like yours or are much worse than yours. This will give you support and the courage to go on. The sense of having similar people around you is often a powerful motivator in itself.
Also, you'll be able to talk to them about your situation without any embarrassment, cause they are the people who have gone through it-they will understand.
Second, if you're in doubt regarding anything related to your mother's illness, these people will be able to help you by sharing their experiences, i.e. what they did in similar situations, etc.
Third, you'll make friends. Yes, this is the place where you'll be able to make true friends. That's because they already know what you're going through-you already have something very important in common. This will ease your feeling of loneliness and helplessness.
Even if you're unable to find such a community near you, you can join an online community.
Also, you can post your questions in yahoo answers. Phrase it like this: "My mother is ill with cancer. It's getting worse. What do I do?" Trust me, within hours you'll get about 20 replies. In those replies you'll find how many other people have suffered what you're suffering, how they've handled it, and above all, how much they feel for you, and want to give you support for being someone like them. (This happens on Yahoo answers. I've seen this.)
7. If possible, try to find some time for yourself. It can be a very short period of 20 minutes or half an hour. This is when you'll do what you love, or something that will help your mind relax. You can watch TV for a while, read your favorite books, or listen to calm, soothing music. This will help you recharge yourself, especially at the end of the day, if you feel all your energy has drained out.
When someone is going through a difficult situation, taking your mind off the current problem for a few minutes often helps.
8. Most importantly, don't EVER become negative