help please

i'm 15 my mums been diagnosed with bone cancer, what do i do. i feel so alone, i have nothing to do with my dad and my aunties live too far away and i rarely talk to them and they both have 3 children of their own, my granny and grandad are way to ill to look after me, if my mum dies what do i do. i have GCSEs and i can't focus on a thing since 18months old it's been just my mum and i and i can't imagine what it's going to be like without her.