I've not lost a child, but I fear it all the time because I was diagnosed with cancer only a few weeks postpartum with my second child. I know all too well that life can unexpectedly change.
No one can tell you how to grieve, and people seem afraid to talk to you when you're in a difficult place. I was talking to a former colleague who was ranting about her day, and she was really embarrassed when she realized how trivial it was vs. my chemo treatments at the time. It didn't bother me, I didn't mind dealing with people's real worlds.
Mother Nature is wise. ~1/2 of all pregnancies naturally terminate because the baby will not be able to survive the pregnancy or the birth. We get so emotionally attached when we want something so dearly, and our instincts rule when we lose it.
What I learned about cancer is that my normal pessimistic point of view changed drastically. I started seeing all the good in everything and really started focusing more on what was present and important. If possible, use your grief for good - let it be a means to dedicate all your energies into your 2 children, helping other people cope with loss (once you're past this stage) and perhaps trying for another child if that's what you really want (or adopting one).
For me, survivorship was one of the hardest parts of dealing with my situation. I finally had to see a therapist to help put things into perspective. I learned that my 36 year-old cousin has a serious cancer diagnosis. His daughter is 3 weeks old. He may not survive more than a few years if statistics are true. I struggled all last week with my own diagnosis and my health currently being well.
Good luck. I hope you find peace soon. In the meantime, try to use your energies to be the best mother, wife, friend, daughter possible and cherish each day you do have.