Cancer killed my twin

My 14th birthday is approaching quickly and I am all to aware of the fact that my twin Danny isn't here to celebrate it with me. Danny died just under 6 years ago of a cancerous brain tumour. He was diagnosed when we were 3 but went into remission so when it relapsed 3 years later, he sadly wasn't strong enough to beat it. We share our birthday with one of the fittest boys in my year as well as my tutor, so everyone knows it's my birthday on Monday. People come up to me and say 'It's your birthday on Monday, isn't it?' and my reply is 'Please don't remind me', yet no one knows why- I'm a very private person and birthdays just bring the memories flooding back. Seeing your twin pale and throwing up; on a drip struggling to breath.. I have started to tell people about my brother- i mentioned him in a French writing assessment and my teacher said 'I didn't know you had a brother..?' and I just stand there smiling until I can mange the words 'He D-died'. The shock on people's faces when I tell them my story is unreal. How I was ironing for a family of 5 by 7 and took up the role of family cook by 8 just so my parents could concentrate on Danny. I don't regret it, not for a moment, I just feel like my childhood was stolen too soon and that it's not fair, but then again life's not fair. The problem is though, that on #Monday I will force myself to go into school, when all I want to do is curl up in a ball with a picture of us and cry myself to sleep. People ask me 'Aren't birthdays suppose to be happy days?' and I say to them 'Yes' and they reply with 'Why aren't you happy then'. That's when I sit there lost for words, because I have the tears rolling down my face, yet I still manage to say 'I'm fine'. If anyone can give any advice on how to get through this day, I would love to know, as they say it gets easier with time, but in all honesty, time just makes the pain more apparent.