Really sorry you are going through this. Do you have anyone to talk to? Other family members or at school? Does school know about your mum? As they will be able to offer you some support. Don't bottle it all in you need to talk. 

I'm 50 and I often don't know what to do either and struggle to focus at work - I hate seeing my husband been made so ill by treatment, even though I know it is key to making him well again. It was worse for the first few months - 9 months in I think am dealing with it better (most of the time).

Definitely let your tutor, or SENCO, or another teacher you like, know what is going on at home at the moment. There will be someone who you can chat to regularly, and who can make sure your subject teachers are on board to help you keep your school work going through all of this. My sons' school even had a club for young carers.

You need some help to keep your normal stuff going, which will help with your focus and emotions, and school is probably the best place to get that. Cancer treatment goes on so long, and affects every day, it just seems to take over. But it won't be forever. Your school work is important too, for your future - I'm sure your Mum would agree - so do be brave and ask them for some help.

I work in the resource department of a secondary school, but in Ireland, so I'm not sure about the British system. I would say though that your reactions are absolutely normal. Heck, I found it hard to concentrate at work after my dad died and there wasn't the same worry there, as the worst had happened. It sounds like you might be concentrating so much on being mature and responsible and helpful at home that the stress is coming out at school.

I don't know if it would be possible for you to have a period or two a week of resource/nuture. Just a period where you could maybe get a start on your homework or just get a break from class. My school has a lot of resources due to our designation, so yours may not have the same options.

Really sorry to hear you are going through this and please remember you don't have to be strong all the time. You still are the kid in your family and while you're not a little child any more, you are still very young to be dealing with all this.

Your post struck a very large cord with me. I too have a 14 year old, and her mum too is in the same position as your mum.

We have been very honest with her and she seems to be handling it better because she knows the facts and we're not sugar coating anything. She gets told what we get told, without exception.

If you feel you're being fed the truth, then hopefully that does give you some confidence/comfort that you  know what the rest of the people surrounding your mum know. There's no second guessing.

No one can fix anything other than the doctors, so don't feel bad that you can't fix it. It's nothing you are doing or done that is causing your mum pain. The best help you can give your mum is just listen to her when she wants to talk. If people feel they are being listened to, that can be as potent as any treatment they may receive. Mental health is important too. For yourself, has anyone mentioned McMillian nurses? They are there for you too, not just your mum. Even if it's just to vent, then I would at least try them once. It may not be for you, but you will never know otherwise.