I feel so lost and alone. is it part of depression?

Probably : You should visit your doctor and have a discussion about what is bothersome . You might need medication and/or counseling.

Possibly : Depression includes many symptom incl depressed mood, loss of pleasure, emptiness, thoughts of death, loss of pleasure, etc. On the other hand the symptoms you mention could be related to grief and/or loneliness due to little contact with others. Consider seeing a counselor to discuss your feelings and to determine the best course of action.

Depression: If you have other symptoms of depression it is best to have it evaluated.