I am so sorry to hear about your mum and how badly this is affecting you. It is such an emotional drain and people find it particularly hard just after the diagnosis when they are waiting for treatment and the future seems totally uncertain and you don't know what to prepare yourself for. You are clearly feeling very low these days and it is very worrying that you have begun to self harm. You say that you have started self harming AGAIN, indicating that this has happened before. Self harming is a very serious matter and it is good that you are taking this seriously and have taken the first step in writing to us. When you feel down it is easy to just let things slide and it can be very hard to make an extra effort in doing something about it.
However, you really should talk to someone face to face about how you feel. Unfortunately riprap has not got the right kind of expertise for such a serious matter but there are other organisations who are dealing with young people in your situation. I strongly ask you to make contact through them so that you can get the help you so desperately need, either face to face, or at least via a telephone helpline. This is something you can NOT keep to yourself - you MUST talk to someone about it, PLEASE! You seem to have very little self confidence and are thinking very low thoughts about yourself, being useless and not helping anybody. Just by writing to us shows that you are a very caring person with a strong wish to help people and I am sure you are being very hard on yourself and probably think that nothing is good enough. I am sure you are doing your very best and are a very good support for many people - you just don't see it yourself.
I have listed some organisations below that hopefully can help you better with your immediate issue relating to self harm, so please get in touch and get the help you so desperately need.
You could contact ChildLine, a free, 24-hour helpline for children and young people in the UK. You can call the helpline on 0800 1111 about any problem, at any time - day or night. You can also have a look at their website in general and you can find their self harm section here.
Samaritans is another organisation available 24 hours a day to provide confidential emotional support for people who are experiencing feelings of distress or despair. You can call them on 08457 90 90 90 or have a look at their website.
Young Minds is another organisation where you can find information on mental health issues for young people including depression and self-harm.
I sincerely hope that you will contact someone who have expertise in self harm and get help with what you're going through. Please feel free to get back in touch with us if you need help with with finding the right support for you. Good luck with it all!