Hello Maz, I'm so sorry for your loss.
It sounds like your lovely nan was your rock in a difficult world, so I am not surprised this has hit you so hard. Most of us feel like this when we lose our mum, but clearly your nan was the closest thing you had to a mum, so it probably feels to you like it did for me when my mum died; that the foundations of your life have crumbled from under your feet and you are left not knowing how to go on and feeling like nothing matters anymore, not even you and like the future no longer matters. If that sounds familiar, then please know it doesn't last, but you do have to try to help yourself get through it.
I am a bit over two years on from losing my mum now and it has got better. In a way, you are luckier than me, as you have your family, so I am hoping that is helping you and perhaps they will now be your new foundation for your life. I am on my own, so have found that hard.
My advice is that you have to help yourself through an experience like this. That's a hit and miss kind of process and you just have to keep holding on and keep trying till you find something that helps. For me the first 18 months were the worst and the hurdles you describe do come and go, but it's the little things that got me - still do. What helped has been revisiting places we went to together. That helped bring back memories of better times and those made me smile, even if they also brought tears to my eyes to be there without mum; putting together an album of photos of her that I can look at when I am missing her and (this may or may not help you), but I also joined a class to explore an activity that my mum also used to enjoy, so that it felt like I was doing it in a way for both of us. I did find that helped alot. I found some very understanding and supportive new friends there and it got me out of the house and made me think about something else for a while and helped me see there is still something worth living for and I still go and it still helps me and I still look forward to it every week and I feel this has done me more good than anything else.
The other thing that helped was to write down how I was feeling daily in a journal for a long time. I do it less now, but I notice, that is what you have done a little of here and I hope that helped you, but I think writing does help. It helps you examine your thoughts and feelings and get them into some kind of order and make sense of them. You don't have to show what you write to anyone and you could write it as a letter to your nan, if that helped, but it does seem to help ease the pressure of your grief somehow and you can go back to it at a later date and see how far you have come when you compare it to how you may be feeling further down the line. The other thing I found helped was walking in the park and sitting on a bench to try to absorb and accept all that had happened. It was a calm and peaceful place to do that and having nature around me really helped - still does.
Lastly, you must know that your lovely nan, though she could never have been with you all your life, will never really be gone from you. She was clearly the most important and best person in your life and she helped shape the person you are now, so that has been her legacy to you, to make herself and your experience of knowing her, loving and being loved by her a part of who you are. I am sure you will find as you go forward into your future that she is in a way still with you. You will be able to hear her voice and advice in your head when you have any kind of dilemma. There will be things you will find that suddenly remind you of her and make you smile or laugh as you realise how she would have reacted to something. You will never stop loving her, nor her you, wherever she is now, so that gives you worth and a strong foundation stone for your future.
She isn't here now to help make that future brighter, so it's up to you now to do that for her. She clearly loved you very much and would want the best for you, so you owe it to her to do that for her now and make the most of your life for both of you. This s a terrible time and very slow and painful journey, but all those who have found their way here, will understand exactly what you are going through and I hope you find some support in knowing that.
Wishing you all the best and sending strength and an understanding hug.