I'm so sorry to hear about your loss. It is never easy to lose a loved one. It's not your fault

Everyone has different ways and times of grieving. For some it can take longer than others but it becomes more of a challenge when you become isolated.
Do you have anyone you can talk to about what you are feeling and what has happened? The hardest thing about grief is having to deal with it alone. That in itself can make it harder to move forward.
You can move on from this. It takes time, support and being gentle with yourself. Take it one day at a time. If you can I would suggest setting small goals for the day to achieve (whether that be around your own care - eating, showering, going for a walk, or building relationships). Things that you can do and slowly build on those goals. Find things that help you to relax and feel slightly better. In time the agonizing grief can fade and you can move forward.
Moving forward doesn't mean forgetting your grandmother or the memories you shared either but finding ways to incorporate them into your life now. They can still hurt at times but slowly they become good memories again of the times you had together. It can really help to share those memories with other family and friends if they are open to it.
I'm thinking of you.