Oh, OP. I'm sorry you're feeling so sad. It really isn't weird at all. My own mum died when I was 6 and I didn't grieve until I became a mum myself either. I wasn't able to actually as my Dad just shut down at the time and she was never mentioned again. We moved away from family so it was if she had never existed. I took my lead from him, just buried it all and got on with life.
Becoming a mum opened the flood gates and all the pent-up, raw emotion came surging out. It was tough. I felt so irrationally angry with her for leaving me, angry with my dad for the way he handled it, sad for myself and devasted for her. I realised how utterly terrified and distraught she must have felt at the idea of leaving me.
A book that helped me at the time was The Courage to Grieve by Judy Tatelbaum. I remember one piece of advice from it which said to imagine she was in front of me and say aloud everything I needed to. I tried it and sobbed my heart out. It was very cathartic.
I then suffered from health anxiety for several years, terrified that I would die young too and leave my children. It intensified when I was the same age as my mum was when she died and also when my children were the age I was when I lost her. I really grieved then for the little girl I was. I don't get the health anxiety (much) anymore but sometimes a wave of grief will catch me unawares and I have a little cry.
I'm not far off fifty, nearly twenty years older than she was but I will always feel like that motherless little girl to some extent. I agree with the way PPs have described grief as life-long. It took me a long to accept that I will always feel the loss. It's something I have to live with. I've tried therapy a couple of times but never stuck with it for long. I'm thinking I might give it another go as transitioning into perimenopause seems to be raking some of it back up again.
One thing that gives me solace is I know how much love I poured into my own children with every cuddle, kiss, every moment I was with them when they were young. I'm pretty sure my mum would have done the same, even if I can't really remember her. So although I've not had her with me, I like to think that she gave me a lifetime of love in the short time we did have together.
to all those who have lost a parent, at whatever age.