Struggling to cope.

I feel like I could have written this post myself. Everything you describe is exactly how I felt when my mum succumbed to cancer last summer, nine weeks after her diagnosis. 
I just couldn’t manage anything other than existing day by day. I was so lost without her, so unsure of my reactions to her passing and unable to work effectively. 
Like you, my work was very supportive, even though I wasn’t terribly effective. 
I spoke to her every day for the last year of her life. Living two hours away, I couldn’t see her as often as I wished but those phone calls meant so much to me and I’m still a bit lost every evening at the time I’d usually call her. 
I didn’t manage my grief very well and isolated myself from friends and family. I couldn’t speak about her and didn’t want to see people as I knew that’s what they’d want to talk about. I guess covid had its benefits as it allowed me to hide away. 
Eventually, I found an outlet. For me, it was therapy. I needed someone completely separate from the situation. It’s made me realise that there’s no rule book on how to manage your grief. It is what it is. There’s nothing wrong with the way you’re feeling right now. You’ve literally just been through one of the most traumatising experiences any of us will ever go through. Your brain is trying to process that and it’ll take some time to get through it. 
You won’t feel it at this stage but I think you’re doing ok in the circumstances. You’re reaching out and asking for help. You’re acknowledging your feelings and how they make you uncomfortable. That seems like a good thing to do. 

I used to hate all the well-meaning snippets of advice you’d get. Time’s a healer and all that is unlikely to be particularly helpful right now. I’m 7 months into my grief and there are days where it’s still very painful. I do know though that I’m in a better place for having shared my thoughts with people who can help. I watched a movie the other day and there was one line that really struck a chord with me. It was something like “the grief at the loss never goes away but it won’t always feel so heavy”. 

I am so sorry your mum is no longer around. It sucks.