In this time of "new age" always being happy you miss an important part of your emotional growth. As long as you are in human form you will have variations in how you feel. Feelings are not good or bad - they are an indicator of what you are thinking and how you experience anything. Feelings have an energetic component and need to move through you. When your feelings remain trapped/suppressed you begin to experience physical and mental ailments.
Grieving comes in stages and may last a long time - it's okay. Just know feeling and releasing by crying/talking/writing/creating is the first pill to reach for - learn how you need to express. Your joy and growth will then follow.