I'm so so sorry for your loss, please allow yourself to grief - it's still early days yet, and there's no greater loss than a mother. 
My mum passed away last March, similar to your situation, she was diagnosed with bowel cancer in Feb 21, within 6 weeks she had passed away. It all happened so fast, and even now I still struggle to comprehend everything that happened, so quickly. 
But I've learnt that it's okay to feel like this, my mum was my mum for 27 years, so I can't possible be healed within 14 months. It will take a lifetime to heal.

A quote I read, that puts it all into perspective, Andrew Garfield: 

"I hope this grief stays with me because it's all the unexpressed love that I didn't get to tell her". 

I'm so so sorry for your loss, please allow yourself to grief - it's still early days yet, and there's no greater loss than a mother. 
My mum passed away last March, similar to your situation, she was diagnosed with bowel cancer in Feb 21, within 6 weeks she had passed away. It all happened so fast, and even now I still struggle to comprehend everything that happened, so quickly. 
But I've learnt that it's okay to feel like this, my mum was my mum for 27 years, so I can't possible be healed within 14 months. It will take a lifetime to heal.

A quote I read, that puts it all into perspective, Andrew Garfield: 

"I hope this grief stays with me because it's all the unexpressed love that I didn't get to tell her".