Hiya again, I'm really sorry for what you are going through at work but at least you can let it out by talking about it here. Maybe you are good at your job and your feelings are making you feel useless or you are finding it too hard and need a little help. Could you confide in a co-worker that you are friendly with?
I know the feeling regarding missing your sisters, I miss my lil sis (she's away at college), i miss the person she once was, now she doesn't bother with me and it hurts.
You are right, you must remain positive and try and see the light. Even if you feel you won't fit in, carry on and accept that by getting help such as counseling and medication.
I really do feel for you, keep talking to us here if it helps.