So sorry to hear of your loss of your mum, Sarah. I lost my own mum a little over two years ago and I still miss her every day. I remember the feeling you describe and I think we all go through similar feelings of feeling lost and alone. There is no one like your mum and however long you have had to 'prepare yourself' for the worst, it is still a shock when it happens. It's a rocky road to recovery with many a slippery slope along the way, but what I found to cling on to was the thought that my mum loves me and would still want the best for me, even if she isn't here to make it happen anymore, so I have to learn to do that on her behalf now and that has slowly led me forward into a new life and helped me make the best of things. It will take time, but our lovely members here will all understand what you are going through and will help however we can. You are not alone.
If you can manage to remember to eat and drink enough and take care of yourself a little, that will probably be quite enough to cope with for now. I did find it helped me to have flowers to look at and their scent to smell when I was where you are now. It reminded me that there is still beauty and goodness in the world and something worth fighting to live for again. Be patient and gentle with yourself. Recovery and finding a way forward is a slow and difficult process, but it can be done. Just take it a day at a time. Wishing you well and sending you a huge understanding hug.