Be kind to yourself
There are days when you're going to be happy and days when you're going to be sad. During one of my "big losses" I remember writing at the beginning of each entry in my diary if that day I had cried or not. After three days in a row not crying I would be very disappointed when on the fourth day I had cried.
Grief is a process of which we have no control.
Sometimes we manage to have a "normal" day, and at other times something triggers a memory and before we know it we're crying on the floor. This is especially true in the first weeks or even months.
If you feel like crying then go ahead and do it. Don't force yourself to swallow your feelings.
If for some reason you can't allow yourself to cry right on the spot (because you're at work, for example), excuse yourself, go to the bathroom and do it there.
Don't judge or punish yourself for crying. Talk to a friend about how you feel.