I can honestly say that I know what you are feeling. I lost my brother 3 years ago in an automobile accident, my father 2 years ago and my mother 6 months ago. That was all the family I had. Well, I do have a 15 year old son and a 21 year old daughter, but thats not quite the same. Sometimes you just feel so all alone, no one left to talk to, no one to call and say say "do you remember when..." I do somewhat the same thing as you - I will pick up the phone to call mom, but I know she won't answer. I can only imagine the last words she spoke to me before she died, "I love you too..."
I thought I was selfish for feeling the way I do, wanting them here and for feeling alone, I didn't realize there were others like me. I am sorry for the pain you are feeling, and if you ever want to talk I am here, I know I'm not mom but...