Sorry about your loss Billy .
Just over six years ago I was fighting with the same feelings. Why couldn't I cry over my Mother? It bothered me so much I spoke to my Doctor who suggested going to see a grief counselor. She suggested something that worked for me, so I am only suggesting it for you if you want to.
Find a friend, usually better than a family member that you trust and let them know what you are doing. Ask them if you can tell them what your mother meant to you. If they are a true friend and worth your trust, they will understand what you are doing.
Then, unlike a book, start talking about what she meant to you. Talk about the good and the bad. I'm sure more good will come out in the end. Try to explain how she shaped you growing up and what she always did to make you feel special. Don't follow an agenda or plan. Just let it come out as it does. Don't try to edit yourself, the emotion of the situation will carry you on fine. Think of the things and share the things that made her your mom. Be proud of her and let that reflect in what you are saying.
Needless to say this worked for me. Ever since, I have to admit I now get a little emotional whenever talking about her, or even writing this.
You will know when you need that good long cry. Just find someone that will listen and know they will support you through this.
But Zombie is right, there is no rules. Do what feels right at the moment.
Good luck (hug)