Both of my parents are gone. I lost my Mom when I was 23 and my Dad 18 months later, just shy of my 25th birthday. It's been nearly a decade since my Mom died (8 years for Dad.) It's hard to believe it's been that long.
My mother and I had difficulties in our relationship (Looking back mainly because she hit menopause the same time I hit puberty) and we were just starting to get along really well when she passed. It was so painful, still is, to think of all the things I missed; she missed. At first I really beat myself up that I didn't cherish her more while she was here.
I was incredibly close with my Dad. For several months I would pick up the phone only to remember that I couldn't just call him. It was hard for many years. Aside from the loss I felt very isolated. He really was my best friend.
I can't say that the grief will ever go away. It really doesn't. But, time does soften it some and the tears won't come so often. The pain will dull. I realize this isn't helpful to you right now, but given time to grieve at your own pace it'll get easier to deal with. No, easy is the wrong word. I guess you just get more used to it.
Allow yourself to grieve. Reach out to the rest of the family and help each other through this. It's an excruciating thing to have to go through.
I like what EZMONEY said about doing something to honor your Mother. I try to do little things to carry on the memory of my parents. I make family recipes, listen to the music they liked, I share their stories with my husband (whom they never met,) etc. They may be gone, but they are not forgotten. I think that's all anyone can ask for.
EDIT: I just remembered a book that was very helpful to me in my grieving process. It's called
A Grief Observed and is by C.S. Lewis. He wrote it after his wife died. I remember my sister giving it to me since it had helped her as well.