A lot of people have experienced death of close friends and family members. It effects different people in different ways.
I know it feels like no one understands what it is like for you and its easy to get angry when people seem to think they do understand or that they know what youre going through when they probably dont.
But the truth is, they are just trying to help you.
They want to make you feel that you arent alone, that you're not the only one who has ever felt like this.
And you arent.
You must have only been very young, and there is nothing you could have done that would have stopped this from happening. So try not to blame yourself for anything, you have no reason to feel any guilt what so ever, your mum knew how much she meant to you, mums have a way of knowing things like that.
Like Kolte said, just think about all the good times you had with your mum. If youre worried about forgetting things, maybe you could get a diary and right them down. So when youre feeling down, or you find yourself thinking about your mum, you can read about all the good times you had together and you can smile about them.
About your dad, can i ask if you and him ever spoke about your mum after she had died?
You dont have to answer if you dont want to, its fine.
I dont know what your relationship is like with him, but maybe you could talk to him? Or if you dont feel you could bring that up with him, maybe give him something/leave something lying around that youve written about how you're feeling about everything so he can read that. Sometimes its easier to write it than to actually say it.
The other person you could talk to is your doctor. I dont know if you have already or if you would want to, but sometimes it can really help you deal with things.
If that sounds like too much, maybe you could call a helpline? Just talking about your mum and your feelings in anonymity can help lead onto to other things.
Anyway, I hope you feel better about everything really soon.
Its tough, but I know you can pull through.