I am so isolated and sad since my mother died. The pain from this loss is sometimes unbearable. Am I depressed?

Death of a loved one is a significant emotional loss.  Grief and depression can sometimes look alike.  Grieving is normal and natural, and is not depression.  It is likely that once you commit to grief counseling and get the tools you need to reconcile your loss, the sadness and isolaltion will be reduced greatly or completely go away.