Hello FrankieF; welcome to the forum.  I am so sorry that you have lost mum and that her final weeks were so distressing for you.  Bearing in mind that I really don't know anything about the interaction your mum had with her GP but it could just have been that the symptoms which your mum presented were not then recognisable as lung cancer.  I have lost several friends to lung cancer and one of the things I have observed is the huge variation in lifespan these people showed when at the same stage.  I am not just talking about a difference of weeks but my son's father deteriorated and died very quickly - six weeks from diagnosis  - while a family member has been at Stage 4 for getting on for 18 months and is still getting around although not as well as she was when first diagnosed.  When you say your mum was sedated before she died could it have been because she was distressed or in pain?  If this was not the case you may well be able to ask the question of the hospital even now as it will have been recorded on her notes. 

You must grieve in your own way. Painful though it must have been for you it will have been a great comfort for your mum to have you close when she died.  I do hope that you have family and friends with whom you can share your feelings.  There is no right or wrong way to grieve; I "talked" to my mum every day when she first died, keeping photos and other bits and pieces most of which I still have (she died in 1984).  Still do sometimes.    It is not reasonable to expect grieving relatives to just get over the death of a parent - for heavens sake they have been there all your life and it is going to take time and grieving before your life can move forward.  You are never the person you were before your mum died and you carry your love and memories within you for the rest  of your life.   Please do come back and chat further with us if you want to do so.  Annie