Hello im looking for some advice to get me through

Last Tuesday I went round my mums to help her with the housework after I dropped my children to school as she has been unwell for a week . She had spoke to the gp who thought it was food poisoning or a bug and give her antibiotics.  My mum is old school and only calls the gp if she is bad. She had a minor heart condition and asthma too.

Alway as I walked in the house I know something was wrong. I run up to her room and she was lifeless on the bed. I call an ambulance and started cpr. Unfortunately it was too late. So for the last week my brother and I and the gp thought she has a heart attack. The post mortem came back today with no cause of death but they found lung, liver, emdrometis tumours and a uterus polyp. They have been sent for testing but they said they think it was mostly definitely cancer. 

I honestly don't know how I felt right now im heartbroken (my dad died of cancer 3 years ago and my nan died of lung cancer at the same age as my mum). But its turning to anger. For example my mum kept going to the doctors about her cough and her inhalers not work just for them to say lose weight,  she was so fed up with them she stop going 6 months ago. 

I dont want to blame anyone but she spoken to the gp the night before she died saying about the pain in her stomach, vaginally bleeding, tiredness, ribs hurting and no energy and the antibiotics not working and as for sleeping tablets to help her sleep. He just said OK.

I just don't know how to deal with this xx